selftests/bpf: Add sockopt case to verify prog_type

Make sure only sockopt programs can be attached to the setsockopt
and getsockopt hooks.

Signed-off-by: Stanislav Fomichev <sdf@google.com>
Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/r/20240426231621.2716876-4-sdf@google.com


Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>