mission: be more intelligent about saying that we are on a mission landing

- previously the decision of being on a landing pattern was taken by just
looking at the current mission index. However, even if the current mission
index indicates a landing pattern the vehicle could be at an arbitrary location, far
from being established on the pattern.

Signed-off-by: RomanBapst <bapstroman@gmail.com>

src/modules/navigator/navigator_main.cpp

@@ -563,9 +563,14 @@ Navigator::run()
 
 					}
 
-					// if RTL is set to use a mission landing and mission has a planned landing, then use MISSION to fly there directly
-					if (on_mission_landing() && !get_land_detected()->landed) {
+
+					if (!rtl_activated && _rtl.initialClimbDone() && get_mission_start_land_available()) {
 						_mission.set_execution_mode(mission_result_s::MISSION_EXECUTION_MODE_FAST_FORWARD);
+
+						if (!getMissionLandingInProgress()) {
+							start_mission_landing();
+						}
+
 						navigation_mode_new = &_mission;
 
 					} else {