NTP: use sntp app from lwip on latest Cores, replace ntpclientlib

[mcspr]

subj

fix #1380 (yay)
fix #1517
fix #1629

TODO:

• timebroker. can it be used as scheduler replacement + rpn? experimenting with $tick1m, $tick1h.
  slightly complicated because of restore-last-schedule since rpn is generic and scheduler part would need to iterate over $tick rules. Can use a different rpn context and ruleset / settings, maybe.
• fix lib_deps forcibly linking ntpclientlib + timelib. if not possible, drop 2.3.0 from supported altogether. if it does work, just switch implementations as needed. webui can have ntplegacyVisible hint to hide offending parts or we could also have a separate panel.
• localtime / gmtime make for some weird interactions
• timelib compat types are all over the place. uptime tries to be fancy, so elapsed... need to accept unsigned and not only time_t

[mcspr]

Also something of note that ntpStartDelay needs to be >= 15 seconds. 0 option also works though, bot nothing in-between 0 and 15
Based on RFC, it has to be at least 15s. Having re-checked the code, it never enforces it. Random re-tuned a bit, since it does actually wait. Probably needs further reducing

[Niek]

Nice job 👍🏻
Any improvements in build size after dropping ntpclientlib?

[mcspr]

None, really. Re-enabling scheduler code, travis shows the same size for basic.h build.
+rpnlib -scheduler is ~10KB as noted in the comment
-scheduler is ~4KB, 1KB more than the comment notice
-legacy ntp code (adding tz, removing offsets) in html/js is 240 bytes total

[mcspr]

In general ntpLocal2UTC() makes no sense if it wants to return timestamp. Timestamp itself is already UTC, where localtime modifies tm struct based on TZ when we use it.

Not really looking too portable, since there needs to be a code chunk using libc functions instead of timelib. I guess it can temporarily setenv("TZ", "UTC0"); dowork(); setenv("TZ", "whatever"); if that is enough to apply the change to localtime result, so minute() / hour() / day() work. Scheduler references timestamps a lot, which needs to be refactored to use time struct

[mcspr]

Timelib helpers are working, scheduler days are in order.
Everything builds even with lib_deps referencing NtpClientLib, only a matter of reading platformio documentation more closely on how it parses dependencies.

[mcspr]

Since configTime re-inits sntp, set timezone through tzset(3)

[mcspr]

Dhcp routine will call sntp_init() whenever dhcp server sets ntp option:
#1828
I also wonder if this is the reason that sntp can never be optimised away

[mcspr]

We can't exactly speed-up sntp like NtpClientLib, so idk about this.
Changing ntpServer value also triggers sync

[mcspr]

BTW some benefit of having #if guards in headers is that compilation will fail instead of linker when function is not implemented / supported

[bluexp1]

I am currently using 1.14.1 and ntp fails to get time from the internet, Is there any solution available to make it work with current version or I need to wait for 1.14.2 to get released?

[mcspr]

download the dev branch and use the latest version? or nightly builds to use binaries?
I'd also suggest to use gitter or just open a new issue for any questions, closed issues / PRs are not easy to track for new discussions.