AttitudeControl: let the user set yaw weight directly via parameter

instead of infering the yaw weight from the gains which can lead to
unexpected results depending on the particular vehicle tuning.

src/modules/mc_att_control/mc_att_control_main.cpp

@@ -94,7 +94,8 @@ void
 MulticopterAttitudeControl::parameters_updated()
 {
 	// Store some of the parameters in a more convenient way & precompute often-used values
-	_attitude_control.setProportionalGain(Vector3f(_param_mc_roll_p.get(), _param_mc_pitch_p.get(), _param_mc_yaw_p.get()));
+	_attitude_control.setProportionalGain(Vector3f(_param_mc_roll_p.get(), _param_mc_pitch_p.get(), _param_mc_yaw_p.get()),
+					      _param_mc_yaw_weight.get());
 
 	// angular rate limits
 	using math::radians;