Avoid wifiSleepBegin()

This seems to sometimes hang and trigger a watchdog. which
isn't terrible as we anyway want to reboot, but better shut
down cleanly. Try a different way to stop wifi.

Author: dirkmueller

airrohr-firmware/airrohr-firmware.ino

@@ -1773,7 +1773,8 @@ static void webserver_config() {
 
 static void sensor_restart() {
 #if defined(ESP8266)
-		WiFi.forceSleepBegin();
+		WiFi.disconnect();
+		WiFi.mode(WIFI_OFF);
 		delay(100);
 #endif
 		SPIFFS.end();