selftests/bpf: dummy_st_ops should reject 0 for non-nullable params

Check if BPF_PROG_TEST_RUN for bpf_dummy_struct_ops programs
rejects execution if NULL is passed for non-nullable parameter.

Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/r/20240424012821.595216-6-eddyz87@gmail.com


Signed-off-by: Alexei Starovoitov <ast@kernel.org>