multicopter: minimize dt jitter by using estimate timestamp_sample

src/modules/flight_mode_manager/FlightModeManager.cpp

@@ -99,7 +99,7 @@ void FlightModeManager::Run()
 	vehicle_local_position_s vehicle_local_position;
 
 	if (_vehicle_local_position_sub.update(&vehicle_local_position)) {
-		const hrt_abstime time_stamp_now = hrt_absolute_time();
+		const hrt_abstime time_stamp_now = vehicle_local_position.timestamp_sample;
 		// Guard against too small (< 0.2ms) and too large (> 100ms) dt's.
 		const float dt = math::constrain(((time_stamp_now - _time_stamp_last_loop) / 1e6f), 0.0002f, 0.1f);
 		_time_stamp_last_loop = time_stamp_now;