aom: Document sframe_mode setting is not implemented

SDL Commits
1 
From 7b24d44e6d32dd8c27089956bf9094378caf51d8 Mon Sep 17 00:00:00 2001
From: Wan-Teh Chang <[EMAIL REDACTED]>
Date: Tue, 6 Aug 2024 14:38:59 -0700
Subject: [PATCH] Document sframe_mode setting is not implemented

Change-Id: Iafad26f05e969b8940103e26e9cd1f91505f1c00
---
 aom/aom_encoder.h | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/aom/aom_encoder.h b/aom/aom_encoder.h
index bdedf48581..f4c653b928 100644
--- a/aom/aom_encoder.h
+++ b/aom/aom_encoder.h
@@ -802,6 +802,8 @@ typedef struct aom_codec_enc_cfg {
    *     S-Frame.
    *
    * Otherwise: the considered frame will be made into an S-Frame.
+   *
+   * \attention Not implemented.
    */
   unsigned int sframe_mode;