rtl: keep rtl altitude below max altitude

land_detector: delete unused class enum

src/modules/navigator/rtl.h

@@ -77,6 +77,12 @@ private:
 	 */
 	void		advance_rtl();
 
+	/**
+	 * Get rtl altitude
+	 */
+	float 		get_rtl_altitude();
+
+
 	enum RTLState {
 		RTL_STATE_NONE = 0,
 		RTL_STATE_CLIMB,