Correctly mark MQTT client online

The online tag allows the client to notify the network that it needs the network, thus preventing network shutdown before the client has moved offline.

Firmware/RTK_Everywhere/MQTT_Client.ino

@@ -870,6 +870,9 @@ void mqttClientUpdate()
             millis(); // Prevent MQTT_CLIENT_SERVICES_CONNECTED from going immediately into timeout
 
         reportHeapNow(settings.debugMqttClientState);
+
+        online.mqttClient = true;
+
         mqttClientSetState(MQTT_CLIENT_SERVICES_CONNECTED);
 
         break;