reproduce (this is a W=1 build):
        # https://github.com/cilium/linux/commit/f5e94535d68e170320fa3ee0da5bc9e0fea45023
        git remote add cilium https://github.com/cilium/linux.git
        git fetch --no-tags cilium max/vxlan-bigtcp
        git checkout f5e94535d68e170320fa3ee0da5bc9e0fea45023

        # save the config file
        mkdir build_dir && cp config build_dir/.config
        make W=1 O=build_dir ARCH=x86_64 olddefconfig
        make W=1 O=build_dir ARCH=x86_64 SHELL=/bin/bash net/netfilter/