implemented vtol weathervane yaw control for landing and loiter mission item

src/modules/mc_pos_control/mc_pos_control_main.cpp

@@ -192,6 +192,7 @@ private:
 		param_t hold_max_xy;
 		param_t hold_max_z;
 		param_t acc_hor_max;
+
 	}		_params_handles;		/**< handles for interesting parameters */
 
 	struct {
@@ -442,7 +443,6 @@ MulticopterPositionControl::MulticopterPositionControl() :
 	_params_handles.hold_max_z = param_find("MPC_HOLD_MAX_Z");
 	_params_handles.acc_hor_max = param_find("MPC_ACC_HOR_MAX");
 
-
 	/* fetch initial parameter values */
 	parameters_update(true);
 }
@@ -1263,6 +1263,14 @@ MulticopterPositionControl::task_main()
 				control_auto(dt);
 			}
 
+			/* weather-vane mode for vtol: disable yaw control */
+			if(_mode_auto && _pos_sp_triplet.current.disable_mc_yaw_control == true) {
+				_att_sp.disable_mc_yaw_control = true;
+			} else {
+				/* reset in case of setpoint updates */
+				_att_sp.disable_mc_yaw_control = false;
+			}
+
 			if (!_control_mode.flag_control_manual_enabled && _pos_sp_triplet.current.valid
 			    && _pos_sp_triplet.current.type == position_setpoint_s::SETPOINT_TYPE_IDLE) {
 				/* idle state, don't run controller and set zero thrust */