selftests/bpf: Tests libbpf autoattach APIs

Adds test for libbpf APIs that toggle bpf program auto-attaching.

Signed-off-by: Hao Luo <haoluo@google.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20220816234012.910255-2-haoluo@google.com