AHRS: limit wind speed estimate changes

sudden yaw changes can cause bad wind estimates

libraries/AP_AHRS/AP_AHRS_DCM.cpp

@@ -624,7 +624,9 @@ void AP_AHRS_DCM::estimate_wind(Vector3f &velocity)
         wind.z = velocitySum.z - V * fuselageDirectionSum.z;
         wind *= 0.5;
 
+	if (wind.length() < _wind.length() + 20) {
 		_wind = _wind * 0.95 + wind * 0.05;
+	}
 
         _last_wind_time = now;
     } else if (now - _last_wind_time > 2000 && _airspeed && _airspeed->use()) {