Update Ethernet doc

Author: cuav-chen2

docs/en/advanced_config/ethernet_setup.md

@@ -29,6 +29,7 @@ Supported flight controllers include:
 - [CUAV Pixhawk V6X](../flight_controller/cuav_pixhawk_v6x.md)
 - [CUAV X25 EVO](../flight_controller/cuav_x25-evo.md)
 - [CUAV X25 SUPER](../flight_controller/cuav_x25-super.md)
+- [CUAV X25-MEGA](../flight_controller/cuav_x25-mega.md)
 - [Holybro Pixhawk 5X](../flight_controller/pixhawk5x.md)
 - [Holybro Pixhawk 6X](../flight_controller/pixhawk6x.md)
 - [RaccoonLab FMUv6X Autopilot](../flight_controller/raccoonlab_fmu6x.md)