bpf: add sk_msg prog sk access tests to test_verifier

Add tests for BPF_PROG_TYPE_SK_MSG to test_verifier for read access
to new sk fields.

Signed-off-by: John Fastabend <john.fastabend@gmail.com>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>