virtio-blk: allow block_resize with dataplane

Now that block_resize acquires the AioContext we can safely allow
resizing the disk.

Reported-by: Andrey Korolyov <andrey@xdel.ru>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

hw/block/dataplane/virtio-blk.c

@@ -193,6 +193,7 @@ void virtio_blk_data_plane_create(VirtIODevice *vdev, VirtIOBlkConf *blk,
 
     error_setg(&s->blocker, "block device is in use by data plane");
     bdrv_op_block_all(blk->conf.bs, s->blocker);
+    bdrv_op_unblock(blk->conf.bs, BLOCK_OP_TYPE_RESIZE, s->blocker);
 
     *dataplane = s;
 }