libbpf: support sockopt hooks

Make libbpf aware of new sockopt hooks so it can derive prog type
and hook point from the section names.

Cc: Andrii Nakryiko <andriin@fb.com>
Cc: Martin Lau <kafai@fb.com>
Signed-off-by: Stanislav Fomichev <sdf@google.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>