bpf: Make struct cgroup btf id global

Make struct cgroup btf id global so later patch can reuse
the same btf id.
Acked-by: David Vernet <void@manifault.com>
Signed-off-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/r/20221026042840.672602-1-yhs@fb.comSigned-off-by: Alexei Starovoitov <ast@kernel.org>

include/linux/btf_ids.h

@@ -265,5 +265,6 @@ MAX_BTF_TRACING_TYPE,
 };
 
 extern u32 btf_tracing_ids[];
+extern u32 bpf_cgroup_btf_id[];
 
 #endif

kernel/bpf/cgroup_iter.c

@@ -157,7 +157,7 @@ static const struct seq_operations cgroup_iter_seq_ops = {
 	.show   = cgroup_iter_seq_show,
 };
 
-BTF_ID_LIST_SINGLE(bpf_cgroup_btf_id, struct, cgroup)
+BTF_ID_LIST_GLOBAL_SINGLE(bpf_cgroup_btf_id, struct, cgroup)
 
 static int cgroup_iter_seq_init(void *priv, struct bpf_iter_aux_info *aux)
 {