tools/virtio: fix vringh test

Include missing virtio_config.h

Signed-off-by: Michael S. Tsirkin <[e-mail]>

tools/virtio/vringh_test.c

···
 #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>