bpf: test_maps, only support ESTABLISHED socks

Ensure that sockets added to a sock{map|hash} that is not in the
ESTABLISHED state is rejected.

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>