Increase the avformat mux buffer size to 10 MB.

The previous value, 32 kB, causes formats like WebM to overflow
and split the blocks, which has negative consequences for streaming.
We're unlikely to have a memory crunch in this area, so increase it
to something generous.
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

modules/demux/avformat/mux.c

@@ -115,7 +115,7 @@ int OpenMux( vlc_object_t *p_this )
         strcpy( p_sys->oc->filename, p_mux->p_access->psz_path );
 
     /* Create I/O wrapper */
-    p_sys->io_buffer_size = 32768;  /* FIXME */
+    p_sys->io_buffer_size = 10 * 1024 * 1024;  /* FIXME */
     p_sys->io_buffer = malloc( p_sys->io_buffer_size );
 
     bool b_can_seek;