bpf: sockmap, fix transition through disconnect without close

It is possible (via shutdown()) for TCP socks to go trough TCP_CLOSE
state via tcp_disconnect() without actually calling tcp_close which
would then call our bpf_tcp_close() callback. Because of this a user
could disconnect a socket then put it in a LISTEN state which would
break our assumptions about sockets always being ESTABLISHED state.

To resolve this rely on the unhash hook, which is called in the
disconnect case, to remove the sock from the sockmap.

Reported-by: Eric Dumazet <edumazet@google.com>
Fixes: 1aa12bdf ("bpf: sockmap, add sock close() hook to remove socks")
Signed-off-by: John Fastabend <john.fastabend@gmail.com>
Acked-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>