add landengfail nav state

src/modules/navigator/navigator_main.cpp

@@ -393,6 +393,9 @@ Navigator::task_main()
 					_navigation_mode = &_rtl; /* TODO: change this to something else */
 				}
 				break;
+			case NAVIGATION_STATE_AUTO_LANDENGFAIL:
+				_navigation_mode = &_engineFailure;
+				break;
 			case NAVIGATION_STATE_LAND:
 			case NAVIGATION_STATE_TERMINATION:
 			case NAVIGATION_STATE_OFFBOARD:

src/modules/uORB/topics/vehicle_status.h

@@ -103,6 +103,7 @@ typedef enum {
 	NAVIGATION_STATE_AUTO_LOITER,		/**< Auto loiter mode */
 	NAVIGATION_STATE_AUTO_RTL,		/**< Auto return to launch mode */
 	NAVIGATION_STATE_AUTO_RTGS,		/**< Auto return to groundstation on data link loss */
+	NAVIGATION_STATE_AUTO_LANDENGFAIL,	/**< Auto land on engine failure */
 	NAVIGATION_STATE_ACRO,			/**< Acro mode */
 	NAVIGATION_STATE_LAND,			/**< Land mode */
 	NAVIGATION_STATE_DESCEND,			/**< Descend mode (no position control) */