[WiFi] Perform wifi disconnect on disconnect event.

See esp8266/Arduino#5912

Author: TD-er

src/ESPEasyWiFiEvent.h

@@ -108,6 +108,10 @@ void onDisconnect(const WiFiEventStationModeDisconnected& event){
   }
   lastDisconnectReason = event.reason;
   wifiStatus = ESPEASY_WIFI_DISCONNECTED;
+  if (WiFi.status() == WL_CONNECTED) {
+    // See https://github.com/esp8266/Arduino/issues/5912
+    WiFi.disconnect();
+  }
   processedDisconnect = false;
 }