vhost-user-blk: Only start vhost-user backend with the first kick

We should only start vhost-user backend at the first kick for
virtio 1.0 transitional devices.
Signed-off-by: NXie Yongji <xieyongji@baidu.com>
Signed-off-by: NZhang Yu <zhangyu31@baidu.com>
Message-Id: <20190320112646.3712-5-xieyongji@baidu.com>
Reviewed-by: NMichael S. Tsirkin <mst@redhat.com>
Signed-off-by: NMichael S. Tsirkin <mst@redhat.com>

hw/block/vhost-user-blk.c

@@ -239,8 +239,7 @@ static void vhost_user_blk_handle_output(VirtIODevice *vdev, VirtQueue *vq)
     VHostUserBlk *s = VHOST_USER_BLK(vdev);
     int i;
 
-    if (!(virtio_host_has_feature(vdev, VIRTIO_F_VERSION_1) &&
-        !virtio_vdev_has_feature(vdev, VIRTIO_F_VERSION_1))) {
+    if (!vdev->start_on_kick) {
         return;
     }