Download realtek r8125 linux driver from official site
https://www.realtek.com/component/zoo/category/network-interface-controllers-10-100-1000m-gigabit-ethernet-pci-express-software
Unpack source file
Replace orginal Makefile with this file
Put this source to 'package' folder of OpenWRT SDK
Build(make menuconfig, make defconfig, make)
kfc2008520/openwrt-r8125
Realtek 2.5G Gigabit Ethernet RTL8125 / RTL8125B(S) PCI-e Driver for Openwrt
CMIT