selftests/bpf: Convert few tests to light skeleton.

Convert few tests that don't use CO-RE to light skeleton.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20210514003623.28033-19-alexei.starovoitov@gmail.com