Rover: Send a heartbeat on mode change

APMrover2/system.cpp

@@ -268,6 +268,7 @@ bool Rover::set_mode(Mode &new_mode, mode_reason_t reason)
 
     control_mode_reason = reason;
     logger.Write_Mode(control_mode->mode_number(), control_mode_reason);
+    gcs().send_message(MSG_HEARTBEAT);
 
     notify_mode(control_mode);
     return true;