reproduce:
        # https://github.com/isilence/linux/commit/30cb7b1a2b1cef31c7eebd4f57f56b33d2f418e0
        git remote add isilence https://github.com/isilence/linux
        git fetch --no-tags isilence zc/rx-v4
        git checkout 30cb7b1a2b1cef31c7eebd4f57f56b33d2f418e0
        make W=1 O=/tmp/kselftest headers
        make W=1 O=/tmp/kselftest -C tools/testing/selftests
        make W=1 O=/tmp/kselftest -C tools/testing/selftests/bpf