bpf: Allow bpf_get_current_ancestor_cgroup_id for tracing

Allow the helper to be called from tracing programs. This is needed to
handle cgroup hiererachies in the program.

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20210627153627.824198-1-namhyung@kernel.org

kernel/trace/bpf_trace.c

@@ -1017,6 +1017,8 @@ bpf_tracing_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 #ifdef CONFIG_CGROUPS
 	case BPF_FUNC_get_current_cgroup_id:
 		return &bpf_get_current_cgroup_id_proto;
+	case BPF_FUNC_get_current_ancestor_cgroup_id:
+		return &bpf_get_current_ancestor_cgroup_id_proto;
 #endif
 	case BPF_FUNC_send_signal:
 		return &bpf_send_signal_proto;