Land detector: Detect ground contact separately

This allows to detect ground contact before concluding the system is landed. This allows to disable some parts of the horizontal control system and only control the vertical position to avoid tipping over.
;

src/modules/land_detector/VtolLandDetector.cpp

@@ -71,6 +71,11 @@ void VtolLandDetector::_update_topics()
 	_orb_update(ORB_ID(airspeed), _airspeedSub, &_airspeed);
 }
 
+bool VtolLandDetector::_get_ground_contact_state()
+{
+	return MulticopterLandDetector::_get_ground_contact_state();
+}
+
 bool VtolLandDetector::_get_landed_state()
 {
 	// this is returned from the mutlicopter land detector