8266 hotfix: solving connectivity problems

* it seems that `WiFiUDP.flsuh()` does something completely different from 8266, and  its actually causing WLED to stall on UI calls. So not usable on 8266.
* fixing a few compiler warnings about "comparing signed and unsigned"

NB: its a hotfix, we have to check if there are other problems on 8266. Also its definitely ugly, but it helps as a band aid.

wled00/ntp.cpp

@@ -226,9 +226,15 @@ void sendNTPPacket()
 
 bool checkNTPResponse()
 {
+#ifdef ARDUINO_ARCH_ESP32
   ntpUdp.flush();
+#endif
   int cb = ntpUdp.parsePacket();
+#ifdef ARDUINO_ARCH_ESP32
   if (!cb) {ntpUdp.flush(); return false;}    // WLEDMM flush buffer
+#else
+  if (!cb) {return false;}    // WLEDMM do not flush buffer
+#endif
 
   uint32_t ntpPacketReceivedTime = millis();
   DEBUG_PRINT(F("NTP recv, l="));