selftests/bpf: Extend sockopt tests to use BPF_LINK_CREATE

Run all existing test cases with the attachment created via
BPF_LINK_CREATE. Next commit will add extra test cases to verify
link_create attach_type enforcement.

Signed-off-by: Stanislav Fomichev <sdf@google.com>
Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/r/20240426231621.2716876-3-sdf@google.com


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