ekf2: consolidate airspeed fusion logic and helpers

- pass new airspeed sample around when available
 - can't completely eliminate _airspeed_sample_delayed until resetWind()
called from sideslip fusion is updated

src/modules/ekf2/EKF/drag_fusion.cpp

@@ -50,11 +50,9 @@ void Ekf::controlDragFusion()
 		if (!_control_status.flags.wind) {
 			// reset the wind states and covariances when starting drag accel fusion
 			_control_status.flags.wind = true;
-			resetWind();
-
+			resetWindToZero();
 		}
 
-
 		dragSample drag_sample;
 
 		if (_drag_buffer->pop_first_older_than(_time_delayed_us, &drag_sample)) {