lavf: consider codec framerate for framerate detection

Fixes detection of some TV sample as 24.5 FPS. With the patch applied,
it's detected as 25 FPS.

This is enabled for mpegts only.

libavformat/mpegts.c

@@ -2616,6 +2616,8 @@ static int mpegts_read_header(AVFormatContext *s)
     int len;
     int64_t pos, probesize = s->probesize;
 
+    s->internal->prefer_codec_framerate = 1;
+
     if (ffio_ensure_seekback(pb, probesize) < 0)
         av_log(s, AV_LOG_WARNING, "Failed to allocate buffers for seekback\n");