AP_CRSF_Telem: adjusted flight mode frame length based on actually used bytes

libraries/AP_RCTelemetry/AP_CRSF_Telem.cpp

@@ -817,9 +817,10 @@ void AP_CRSF_Telem::calc_flight_mode()
 {
     AP_Notify * notify = AP_Notify::get_singleton();
     if (notify) {
-        hal.util->snprintf(_telem.bcast.flightmode.flight_mode, 16, "%s", notify->get_flight_mode_str());
-
-        _telem_size = sizeof(AP_CRSF_Telem::FlightModeFrame);
+        // Note: snprintf() always terminates the string
+        hal.util->snprintf(_telem.bcast.flightmode.flight_mode, sizeof(AP_CRSF_Telem::FlightModeFrame), "%s", notify->get_flight_mode_str());
+        // Note: strlen(_telem.bcast.flightmode.flight_mode) is safe because called on a guaranteed null terminated string
+        _telem_size = strlen(_telem.bcast.flightmode.flight_mode) + 1; //send the terminator as well
         _telem_type = AP_RCProtocol_CRSF::CRSF_FRAMETYPE_FLIGHT_MODE;
         _telem_pending = true;
     }