libbpf: add ability to attach/detach BPF program to perf event

bpf_program__attach_perf_event allows to attach BPF program to existing
perf event hook, providing most generic and most low-level way to attach BPF
programs. It returns struct bpf_link, which should be passed to
bpf_link__destroy to detach and free resources, associated with a link.

Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Reviewed-by: Stanislav Fomichev <sdf@google.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

src/libbpf.map

@@ -169,6 +169,7 @@ LIBBPF_0.0.4 {
 	global:
 		bpf_link__destroy;
 		bpf_object__load_xattr;
+		bpf_program__attach_perf_event;
 		btf_dump__dump_type;
 		btf_dump__free;
 		btf_dump__new;