add mqtt connected callback

src/espmega_iot_core.cpp

@@ -370,6 +370,7 @@ void mqtt_connect()
     {
       standalone = true;
       Serial.print("MQTT not connected, continuing in standalone mode\n");
+      mqtt_connected_user_callback();
       lcd_send_stop_bit();
     }
     lcd_send_stop_bit();

src/user_code.cpp

@@ -84,4 +84,8 @@ void timer1_callback()
 
 void ac_changed_user_callback(int mode, int temperature, int fan_speed) {
     
+}
+
+void mqtt_connected_user_callback() {
+
 }

src/user_code.hpp

@@ -24,6 +24,7 @@ void pwm_changed_user_callback(int pin);
 void ac_changed_user_callback(int mode, int temperature, int fan_speed);
 void timer_tick_callback();
 void timer1_callback();
+void mqtt_connected_user_callback();
 void bt0PopCallback(void *ptr);