libavformat.v: add ffio_set_buf_size() for ffserver.

its inevitable with the current API
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/libavformat.v

@@ -10,6 +10,7 @@ LIBAVFORMAT_$MAJOR {
                 ff_rtp_get_local_rtp_port;
                 ff_rtp_get_local_rtcp_port;
                 ffio_open_dyn_packet_buf;
+                ffio_set_buf_size;
                 ffurl_close;
                 ffurl_open;
                 ffurl_read_complete;