Add support for Xiaomi AX1800 Wifi 6 router

Hello @hurjup, I was able to gain SSH access in AX5/AX1800/RA67 with 3.0.34 global stock Xoaimi's firmware using another Openwrt router and the following guide:

Do you have another router with Openwrt installed? This way is the easiest one I found to achieve that goal...