DNSServer: fix improper startup code in WiFi mode

When running on WiFi-AP mode server's start() method returned true while in fact UDP listening socket was never created
Regression introduced in espressif#8760
Closes espressif#10330

libraries/DNSServer/examples/CaptivePortal/CaptivePortal.ino

@@ -39,7 +39,10 @@ void setup() {
 
  // by default DNSServer is started serving any "*" domain name. It will reply
  // AccessPoint's IP to all DNS request (this is required for Captive Portal detection)
- dnsServer.start();
+ if ( dnsServer.start() )
+ Serial.println("Started DNS server in captive portal-mode");
+ else
+ Serial.println("Err: Can't start DNS server!");
 
  // serve a simple root page
  server.on("/", handleRoot);

libraries/DNSServer/src/DNSServer.cpp

@@ -22,10 +22,12 @@ bool DNSServer::start() {
 #if SOC_WIFI_SUPPORTED
  if (WiFi.getMode() & WIFI_AP) {
  _resolvedIP = WiFi.softAPIP();
- return true;
- }
+ } else
+ return false; // won't run if WiFi is not in AP mode, or no WiFi 
+#else
+ return false; // for other non WiFi-AP networking an overloaded method must be used to get device's IP
+ // start(uint16_t port, const String &domainName, const IPAddress &resolvedIP)
 #endif
- return false; // won't run if WiFi is not in AP mode
  }
 
  _udp.close();