introduce data link lost counter

src/modules/commander/commander.cpp

@@ -1477,6 +1477,7 @@ int commander_thread_main(int argc, char *argv[])
 			if (!status.data_link_lost) {
 				mavlink_log_critical(mavlink_fd, "ALL DATA LINKS LOST");
 				status.data_link_lost = true;
+				status.data_link_lost_counter++;
 				status_changed = true;
 			}
 		}

src/modules/uORB/topics/vehicle_status.h

@@ -201,6 +201,7 @@ struct vehicle_status_s {
 	bool rc_input_blocked;				/**< set if RC input should be ignored */
 
 	bool data_link_lost;						/**< datalink to GCS lost */
+	uint8_t data_link_lost_counter;					/**< counts unique data link lost events */
 
 	bool offboard_control_signal_found_once;
 	bool offboard_control_signal_lost;