stream/smb: mark as network stream for --cache=auto

This causes the cache to be enabled with --cache=auto. It was not done
previously because the small cache size 320k actually led to worse
performance. However, with the current default cache size of 25000kb,
caching notably improves performance.

stream/stream_smb.c

@@ -133,6 +133,7 @@ static int open_f (stream_t *stream)
   stream->close = close_f;
   stream->control = control;
   stream->read_chunk = 128 * 1024;
+  stream->streaming = true;
 
   return STREAM_OK;
 }