Geofence - Change from "re-engage geofence failsafe every 10s when

outside the fence" to "engage geofence failsafe on transition". This
way, the pilot is not stucked in the non flight zone and can switch to
a manual mode and fly back or trigger RTL.

src/modules/commander/Commander.hpp

@@ -167,7 +167,7 @@ private:
 	bool _geofence_loiter_on{false};
 	bool _geofence_rtl_on{false};
 	bool _warning_action_on{false};
-	hrt_abstime _last_geofence_violation{0};
+	bool _geofence_violated_prev{false};
 
 	FailureDetector _failure_detector;
 	bool _failure_detector_termination_printed{false};