Compute RTL time and react if lower than flight time

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

msg/CMakeLists.txt

@@ -131,7 +131,7 @@ set(msg_files
 	rc_channels.msg
 	rc_parameter_map.msg
 	rpm.msg
-	rtl_flight_time.msg
+	rtl_time_estimate.msg
 	safety.msg
 	satellite_info.msg
 	sensor_accel.msg

msg/rtl_flight_time.msg

@@ -1,4 +0,0 @@
-uint64 timestamp				# time since system start (microseconds)
-
-float32 rtl_time_s				# how long in seconds will the RTL take
-float32 rtl_limit_fraction			# what fraction of the allowable RTL time would be taken

msg/rtl_time_estimate.msg

@@ -0,0 +1,5 @@
+uint64 timestamp # time since system start (microseconds)
+
+bool valid			# Flag indicating whether the time estiamtes are valid
+float32 time_estimate		# [s] Estimated time for RTL
+float32 safe_time_estimate	# [s] Same as time_estimate, but with safety factor and safety margin included (factor*t + margin)