bpf, selftests: Fix test_maps now that sockmap supports UDP

UDP socket support was added recently so testing UDP insert failure is no
longer correct and causes test_maps failure. The fix is easy though, we
simply need to test that UDP is correctly added instead of blocked.

Fixes: 122e6c79

 ("sock_map: Update sock type checks for UDP")
Reported-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: John Fastabend <john.fastabend@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20210720184832.452430-1-john.fastabend@gmail.com