mavlink: prevent race if shut down immediately

If we do mavlink stop-all right after mavlink start, we do a perf_free
before actually having stopped the threads accessing the perf counters.

src/modules/mavlink/mavlink_main.cpp

@@ -183,9 +183,6 @@ Mavlink::Mavlink() :
 
 Mavlink::~Mavlink()
 {
-	perf_free(_loop_perf);
-	perf_free(_loop_interval_perf);
-
 	if (_task_running) {
 		/* task wakes up every 10ms or so at the longest */
 		_task_should_exit = true;
@@ -205,6 +202,9 @@ Mavlink::~Mavlink()
 			}
 		} while (_task_running);
 	}
+
+	perf_free(_loop_perf);
+	perf_free(_loop_interval_perf);
 }
 
 void
@@ -2458,9 +2458,6 @@ Mavlink::task_main(int argc, char *argv[])
 		}
 
 		perf_end(_loop_perf);
-
-		/* confirm task running only once fully initialized */
-		_task_running = true;
 	}
 
 	/* first wait for threads to complete before tearing down anything */

src/modules/mavlink/mavlink_main.h

@@ -546,7 +546,7 @@ private:
 
 	uORB::PublicationQueued<telemetry_status_s>	_telem_status_pub{ORB_ID(telemetry_status)};
 
-	bool			_task_running{false};
+	bool			_task_running{true};
 	static bool		_boot_complete;
 	static constexpr int	MAVLINK_MAX_INSTANCES{4};
 	static constexpr int	MAVLINK_MIN_INTERVAL{1500};