This script builds nft-fullcone kernel module suitable for OpenWrt official kernel.
It's kernel vermagic is same as OpenWrt official kernel.
So this module is compatible and can be installed directly in OpenWrt official image.
The build process references https://hamy.io/post/0015/how-to-compile-openwrt-and-still-use-the-official-repository/
The patch is derived from https://github.com/wongsyrone/lede-1