bpf: Sync uapi bpf.h header for the tooling infra

Commit 0abff46 ("bpf: Add comment about helper freeze") missed the
tooling header sync. Fix it.

Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
Link: https://lore.kernel.org/r/20250213050427.2788837-1-yonghong.song@linux.dev
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

Author: Yonghong Song

tools/include/uapi/linux/bpf.h

@@ -6019,7 +6019,10 @@ union bpf_attr {
 	FN(user_ringbuf_drain, 209, ##ctx)		\
 	FN(cgrp_storage_get, 210, ##ctx)		\
 	FN(cgrp_storage_delete, 211, ##ctx)		\
-	/* */
+	/* This helper list is effectively frozen. If you are trying to	\
+	 * add a new helper, you should add a kfunc instead which has	\
+	 * less stability guarantees. See Documentation/bpf/kfuncs.rst	\
+	 */
 
 /* backwards-compatibility macros for users of __BPF_FUNC_MAPPER that don't
  * know or care about integer value that is now passed as second argument