bpf: Selftests, add ktls tests to test_sockmap

Until now we have only had minimal ktls+sockmap testing when being
used with helpers and different sendmsg/sendpage patterns. Add a
pass with ktls here.

To run just ktls tests,

 $ ./test_sockmap --whitelist="ktls"

Signed-off-by: John Fastabend <john.fastabend@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: Jakub Sitnicki <jakub@cloudflare.com>
Link: https://lore.kernel.org/bpf/158939736278.15176.5435314315563203761.stgit@john-Precision-5820-Tower