libbpf: Set expected_attach_type for BPF_PROG_TYPE_SK_REUSEPORT.

This commit introduces a new section (sk_reuseport/migrate) and sets
expected_attach_type to two each section in BPF_PROG_TYPE_SK_REUSEPORT
program.
Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.co.jp>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Link: https://lore.kernel.org/bpf/20210612123224.12525-11-kuniyu@amazon.co.jp

tools/lib/bpf/libbpf.c

@@ -9075,7 +9075,10 @@ static struct bpf_link *attach_iter(const struct bpf_sec_def *sec,
 
 static const struct bpf_sec_def section_defs[] = {
 	BPF_PROG_SEC("socket",			BPF_PROG_TYPE_SOCKET_FILTER),
-	BPF_PROG_SEC("sk_reuseport",		BPF_PROG_TYPE_SK_REUSEPORT),
+	BPF_EAPROG_SEC("sk_reuseport/migrate",	BPF_PROG_TYPE_SK_REUSEPORT,
+						BPF_SK_REUSEPORT_SELECT_OR_MIGRATE),
+	BPF_EAPROG_SEC("sk_reuseport",		BPF_PROG_TYPE_SK_REUSEPORT,
+						BPF_SK_REUSEPORT_SELECT),
 	SEC_DEF("kprobe/", KPROBE,
 		.attach_fn = attach_kprobe),
 	BPF_PROG_SEC("uprobe/",			BPF_PROG_TYPE_KPROBE),