Compute RTL time and react if lower than flight time

- Compute RTL time also during RTL
- Calculate correct altitude when finding destination

src/modules/logger/logged_topics.cpp

@@ -83,7 +83,7 @@ void LoggedTopics::add_default_topics()
 	add_optional_topic("px4io_status");
 	add_topic("radio_status");
 	add_optional_topic("rpm", 500);
-	add_topic("rtl_flight_time", 1000);
+	add_topic("rtl_time_estimate", 1000);
 	add_topic("safety");
 	add_topic("sensor_combined");
 	add_optional_topic("sensor_correction");