tools/virtio: fix vringh test

Include missing virtio_config.h

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
diff --git a/tools/virtio/vringh_test.c b/tools/virtio/vringh_test.c
index 9d4b1bc..13e0a76 100644
--- a/tools/virtio/vringh_test.c
+++ b/tools/virtio/vringh_test.c
@@ -7,6 +7,7 @@
 #include <linux/virtio.h>
 #include <linux/vringh.h>
 #include <linux/virtio_ring.h>
+#include <linux/virtio_config.h>
 #include <linux/uaccess.h>
 #include <sys/types.h>
 #include <sys/stat.h>