bpf: Sync asm-generic/socket.h to tools/

SO_DETACH_REUSEPORT_BPF is needed for the test in the next patch.
It is defined in the socket.h.

Signed-off-by: Martin KaFai Lau <kafai@fb.com>
Reviewed-by: Stanislav Fomichev <sdf@google.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>