AP_ADSB: fixed signed int compare compile warning/error and reject >24bit ICAO

- The value is only 24bits anyway so sign conversion does not matter
- also reject ICAO values > 24bits

libraries/AP_ADSB/AP_ADSB.cpp

@@ -346,11 +346,12 @@ void AP_ADSB::handle_vehicle(const mavlink_message_t* packet)
     vehicle.last_update_ms = now - (vehicle.info.tslc * 1000);
 
     const uint16_t required_flags_position = ADSB_FLAGS_VALID_COORDS | ADSB_FLAGS_VALID_ALTITUDE;
-    const bool detected_ourself = (out_state.cfg.ICAO_id != 0) && (out_state.cfg.ICAO_id == vehicle.info.ICAO_address);
+    const bool detected_ourself = (out_state.cfg.ICAO_id != 0) && ((uint32_t)out_state.cfg.ICAO_id == vehicle.info.ICAO_address);
 
     if (vehicle_loc.is_zero() ||
             out_of_range ||
             detected_ourself ||
+            (vehicle.info.ICAO_address > 0x00FFFFFF) || // ICAO address is 24bits, so ignore higher values.
             !(vehicle.info.flags & required_flags_position) ||
             now - vehicle.last_update_ms > VEHICLE_TIMEOUT_MS) {