selftests/bpf: Test case for SEC("?.struct_ops")

Check that "?.struct_ops" and "?.struct_ops.link" section names define
struct_ops maps with autocreate == false after open.

Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20240306104529.6453-14-eddyz87@gmail.com