Extend bpf_obj_id selftest to verify bpf_link's observability APIs.
Signed-off-by: NAndrii Nakryiko <andriin@fb.com>
Signed-off-by: NAlexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200429001614.1544-7-andriin@fb.com