navigator: publish distance sensor mode change request when in RTL landing phase or during mission landing

src/modules/navigator/rtl_mission_fast_reverse.h

@@ -58,6 +58,9 @@ public:
 	void on_activation() override;
 	void on_active() override;
 	void on_inactive() override;
+	void on_inactivation() override;
+
+	bool isLanding() override {return _in_landing_phase;};
 
 	rtl_time_estimate_s calc_rtl_time_estimate() override;
 
@@ -68,5 +71,7 @@ private:
 
 	int _mission_index_prior_rtl{-1};
 
+	bool _in_landing_phase{false};
+
 	uORB::SubscriptionData<home_position_s> _home_pos_sub{ORB_ID(home_position)};		/**< home position subscription */
 };