lavfi: change AVFilterLink.sample_rate from int64_t to int on next bump

There is no real reason for it to be 64bit, it's just a plain int in the
rest of Libav.

libavfilter/avfilter.h

@@ -596,7 +596,11 @@ struct AVFilterLink {
     AVRational sample_aspect_ratio; ///< agreed upon sample aspect ratio
     /* These two parameters apply only to audio */
     uint64_t channel_layout;    ///< channel layout of current buffer (see libavutil/audioconvert.h)
+#if FF_API_SAMPLERATE64
     int64_t sample_rate;        ///< samples per second
+#else
+    int sample_rate;            ///< samples per second
+#endif
 
     int format;                 ///< agreed upon media format
 

libavfilter/version.h

@@ -47,5 +47,8 @@
 #ifndef FF_API_GRAPH_AVCLASS
 #define FF_API_GRAPH_AVCLASS            (LIBAVFILTER_VERSION_MAJOR > 2)
 #endif
+#ifndef FF_API_SAMPLERATE64
+#define FF_API_SAMPLERATE64             (LIBAVFILTER_VERSION_MAJOR < 3)
+#endif
 
 #endif // AVFILTER_VERSION_H