MulticopterPositionControl: prevent velocity integrator filling up from stale acceleration setpoints

When position control is disabled, clear the setpoint properly to prevent stale values. This fixes a bug where switching to position mode in the same control loop as a hover thrust estimate update could fill up the velocity integrator.

src/modules/mc_pos_control/MulticopterPositionControl.cpp

@@ -408,6 +408,7 @@ void MulticopterPositionControl::Run()
 				} else if (previous_position_control_enabled && !_vehicle_control_mode.flag_multicopter_position_control_enabled) {
 					// clear existing setpoint when controller is no longer active
 					_setpoint = PositionControl::empty_trajectory_setpoint;
+					_control.setInputSetpoint(_setpoint);
 				}
 			}
 		}