selftests/bpf: Test struct_ops map definition with type suffix

Extend struct_ops_module test case to check if it is possible to use
'___' suffixes for struct_ops type specification.

Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: David Vernet <void@manifault.com>
Link: https://lore.kernel.org/bpf/20240306104529.6453-5-eddyz87@gmail.com