en-/disable mc position controller using explicit control mode flag

msg/vehicle_control_mode.msg

@@ -2,6 +2,7 @@ uint64 timestamp		# time since system start (microseconds)
 bool flag_armed			# synonym for actuator_armed.armed
 
 bool flag_external_manual_override_ok		# external override non-fatal for system. Only true for fixed wing
+bool flag_multicopter_position_control_enabled
 
 bool flag_control_manual_enabled		# true if manual input is mixed in
 bool flag_control_auto_enabled			# true if onboard autopilot should act

src/modules/commander/Commander.cpp

@@ -3328,6 +3328,14 @@ Commander::update_control_mode()
 		break;
 	}
 
+	_vehicle_control_mode.flag_multicopter_position_control_enabled =
+		(_status.vehicle_type == vehicle_status_s::VEHICLE_TYPE_ROTARY_WING)
+		&& (_vehicle_control_mode.flag_control_altitude_enabled
+		    || _vehicle_control_mode.flag_control_climb_rate_enabled
+		    || _vehicle_control_mode.flag_control_position_enabled
+		    || _vehicle_control_mode.flag_control_velocity_enabled
+		    || _vehicle_control_mode.flag_control_acceleration_enabled);
+
 	_vehicle_control_mode.timestamp = hrt_absolute_time();
 	_control_mode_pub.publish(_vehicle_control_mode);
 }

src/modules/mc_pos_control/MulticopterPositionControl.cpp

@@ -289,7 +289,7 @@ void MulticopterPositionControl::Run()
 
 		PositionControlStates states{set_vehicle_states(local_pos)};
 
-		if (_control_mode.flag_control_acceleration_enabled || _control_mode.flag_control_climb_rate_enabled) {
+		if (_control_mode.flag_multicopter_position_control_enabled) {
 
 			_trajectory_setpoint_sub.update(&_setpoint);