reproduce:
        # https://git.kernel.org/pub/scm/linux/kernel/git/netfilter/nf-next.git/commit/?id=4a15044a2b06748c99a8c8c3c6b3ee0a01f8004d
        git remote add netfilter-nf-next https://git.kernel.org/pub/scm/linux/kernel/git/netfilter/nf-next.git
        git fetch --no-tags netfilter-nf-next for-netdev-nf-next-26-06-07
        git checkout 4a15044a2b06748c99a8c8c3c6b3ee0a01f8004d
        make menuconfig
        # enable CONFIG_COMPILE_TEST, CONFIG_WARN_MISSING_DOCUMENTS, CONFIG_WARN_ABI_ERRORS
        # pip install -r Documentation/sphinx/requirements.txt
        make htmldocs