VehicleControlMode: add flag_control_allocation_enabled

Allows (external) modes to directly publish actuator_{motors,servos}.

src/modules/control_allocator/ControlAllocator.cpp

@@ -359,6 +359,14 @@ ControlAllocator::Run()
 		}
 	}
 
+	{
+		vehicle_control_mode_s vehicle_control_mode;
+
+		if (_vehicle_control_mode_sub.update(&vehicle_control_mode)) {
+			_publish_controls = vehicle_control_mode.flag_control_allocation_enabled;
+		}
+	}
+
 	// Guard against too small (< 0.2ms) and too large (> 20ms) dt's.
 	const hrt_abstime now = hrt_absolute_time();
 	const float dt = math::constrain(((now - _last_run) / 1e6f), 0.0002f, 0.02f);
@@ -641,6 +649,10 @@ ControlAllocator::publish_control_allocator_status(int matrix_index)
 void
 ControlAllocator::publish_actuator_controls()
 {
+	if (!_publish_controls) {
+		return;
+	}
+
 	actuator_motors_s actuator_motors;
 	actuator_motors.timestamp = hrt_absolute_time();
 	actuator_motors.timestamp_sample = _timestamp_sample;