Make rtsp_set_callback() comments available to Doxygen

Originally committed as revision 8257 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavformat/rtsp.h

@@ -76,7 +76,7 @@ typedef int FFRTSPCallback(enum RTSPCallbackAction action,
                            char *buf, int buf_size,
                            void *arg);
 
-/* useful for modules: set RTSP callback function */
+/** useful for modules: set RTSP callback function */
 void rtsp_set_callback(FFRTSPCallback *rtsp_cb);
 
 int rtsp_init(void);