lavfi: move AVFilterLink.frame_wanted_out to FilterLinkInternal

libavfilter/avfilter_internal.h

@@ -67,6 +67,13 @@ typedef struct FilterLinkInternal {
      */
     int status_out;
 
+    /**
+     * True if a frame is currently wanted on the output of this filter.
+     * Set when ff_request_frame() is called by the output,
+     * cleared when a frame is filtered.
+     */
+    int frame_wanted_out;
+
     /**
      * Index in the age array.
      */