Enable SO_REUSE in LwIP and WiFiServer (#1431)

[igrr]

This change enables SO_REUSE in LwIP config, and makes use of it in WiFiServer.
Fixes issue that server can not be restarted if WiFiServer::stop was called while a client connection was active.

[codecov-io]

Current coverage is 42.59%

Merging #2140 into master will increase coverage by 16.29%

@@             master      #2140   diff @@
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  Files            19         19          
  Lines          3634       3634          
  Methods         328        328          
  Messages          0          0          
  Branches        585        585          
==========================================
+ Hits            956       1548   +592   
+ Misses         2513       2086   -427   
+ Partials        165          0   -165   

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[igrr]

Apparently enabling SO_REUSE doesn't add any extra RAM, so this is safe to merge.

sketch                           data     rodata   bss      text     irom0.text   dram     flash
WiFiMulti.ino                    +0       +0       +0       +0       +176         +0       +176    
DNSServer.ino                    +0       +0       +0       +0       +192         +0       +192    
WiFiClientEvents.ino             +0       +0       +0       +0       +176         +0       +176    
BasicOTA.ino                     +0       +0       +0       +0       +192         +0       +192    
ChatServer.ino                   +0       +0       +0       +0       +176         +0       +176    
SecureWebUpdater.ino             +0       +0       +0       +0       +192         +0       +192    
SDWebServer.ino                  +0       +0       +0       +0       +192         +0       +192    
BarometricPressureWebServer.ino  +0       +0       +0       +0       +176         +0       +176    
CheckFlashConfig.ino             +0       +0       +0       +0       +176         +0       +176    
eeprom_clear.ino                 +0       +0       +0       +0       +176         +0       +176    
BasicHttpClient.ino              +0       +0       +0       +0       +176         +0       +176    
UdpNtpClient.ino                 +0       +0       +0       +0       +192         +0       +192    
CardInfo.ino                     +0       +0       +0       +0       +176         +0       +176    
Datalogger.ino                   +0       +0       +0       +0       +176         +0       +176    
FSBrowser.ino                    +0       +0       +0       +0       +192         +0       +192    
WebClientRepeating.ino           +0       +0       +0       +0       +176         +0       +176    
HTTPSRequest.ino                 +0       +0       +0       +0       +160         +0       +160    
Arduino_Wifi_AVRISP.ino          +0       +0       +0       +0       +192         +0       +192    
AdvancedWebServer.ino            +0       +0       +0       +0       +192         +0       +192    
CaptivePortal.ino                +0       +0       +0       +0       +192         +0       +192    
AdvancedChatServer.ino           +0       +0       +0       +0       +176         +0       +176    
Sweep.ino                        +0       +0       +0       +0       +176         +0       +176    
BlinkWithoutDelay.ino            +0       +0       +0       +0       +176         +0       +176    
OTALeds.ino                      +0       +0       +0       +0       +192         +0       +192    
CallSDKFunctions.ino             +0       +0       +0       +0       +176         +0       +176    
eeprom_read.ino                  +0       +0       +0       +0       +192         +0       +192    
mDNS-SD_Extended.ino             +0       +0       +0       +0       +192         +0       +192    
sha1.ino                         +0       +0       +0       +0       +176         +0       +176    
TelnetClient.ino                 +0       +0       +0       +0       +176         +0       +176    
WebUpdater.ino                   +0       +0       +0       +0       +192         +0       +192    
drawLines.ino                    +0       +0       +0       +0       +176         +0       +176    
shapes.ino                       +0       +0       +0       +0       +192         +0       +192    
mDNS_Web_Server.ino              +0       +0       +0       +0       +192         +0       +192    
Authorization.ino                +0       +0       +0       +0       +176         +0       +176    
drawRectangle.ino                +0       +0       +0       +0       +176         +0       +176    
httpUpdateSPIFFS.ino             +0       +0       +0       +0       +192         +0       +192    
DumpFile.ino                     +0       +0       +0       +0       +176         +0       +176    
eeprom_write.ino                 +0       +0       +0       +0       +176         +0       +176    
ReuseConnection.ino              +0       +0       +0       +0       +176         +0       +176    
HelloMesh.ino                    +0       +0       +0       +0       +192         +0       +192    
Blink.ino                        +0       +0       +0       +0       +176         +0       +176    
HttpBasicAuth.ino                +0       +0       +0       +0       +192         +0       +192    
HelloServer.ino                  +0       +0       +0       +0       +192         +0       +192    
text.ino                         +0       +0       +0       +0       +192         +0       +192    
WebClient.ino                    +0       +0       +0       +0       +176         +0       +176    
WiFiWebServer.ino                +0       +0       +0       +0       +192         +0       +192    
DhcpChatServer.ino               +0       +0       +0       +0       +176         +0       +176    
UDPSendReceiveString.ino         +0       +0       +0       +0       +176         +0       +176    
SSDP.ino                         +0       +0       +0       +0       +192         +0       +192    
Files.ino                        +0       +0       +0       +0       +176         +0       +176    
TickerBasic.ino                  +0       +0       +0       +0       +176         +0       +176    
DhcpAddressPrinter.ino           +0       +0       +0       +0       +176         +0       +176    
listfiles.ino                    +0       +0       +0       +0       +176         +0       +176    
StreamHttpClient.ino             +0       +0       +0       +0       +176         +0       +176    
ConfigFile.ino                   +0       +0       +0       +0       +192         +0       +192    
OTA-mDNS-SPIFFS.ino              +0       +0       +0       +0       +176         +0       +176    
SimpleAuthentification.ino       +0       +0       +0       +0       +192         +0       +192    
TickerParameter.ino              +0       +0       +0       +0       +176         +0       +176    
WiFiTelnetToSerial.ino           +0       +0       +0       +0       +192         +0       +192    
CaptivePortalAdvanced.ino        +0       +0       +0       +0       +192         +0       +192    
WiFiScan.ino                     +0       +0       +0       +0       +176         +0       +176    
httpUpdate.ino                   +0       +0       +0       +0       +176         +0       +176    
NTPClient.ino                    +0       +0       +0       +0       +176         +0       +176    
drawCircle.ino                   +0       +0       +0       +0       +176         +0       +176    
WiFiClientBasic.ino              +0       +0       +0       +0       +192         +0       +192    
ReadWrite.ino                    +0       +0       +0       +0       +176         +0       +176    
drawNumber.ino                   +0       +0       +0       +0       +176         +0       +176    
WebUpdate.ino                    +0       +0       +0       +0       +192         +0       +192    
WiFiAccessPoint.ino              +0       +0       +0       +0       +192         +0       +192    
WiFiClient.ino                   +0       +0       +0       +0       +176         +0       +176    
TestEspApi.ino                   +0       +0       +0       +0       +176         +0       +176    
WebServer.ino                    +0       +0       +0       +0       +176         +0       +176    
RTCUserMemory.ino                +0       +0       +0       +0       +176         +0       +176