libbpf: Support sk_skb/stream_{parser, verdict} section names

Add section names for BPF_SK_SKB_STREAM_PARSER and
BPF_SK_SKB_STREAM_VERDICT attach types to be able to identify them in
libbpf_attach_type_by_name.

"stream_parser" and "stream_verdict" are used instead of simple "parser"
and "verdict" just to avoid possible confusion in a place where attach
type is used alone (e.g. in bpftool's show sub-commands) since there is
another attach point that can be named as "verdict": BPF_SK_MSG_VERDICT.

Signed-off-by: Andrey Ignatov <rdna@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>