Virtqueue has split and packed, so before setting inflight,
you need to inform the back-end virtqueue format.

Signed-off-by: Jin Yu <jin.yu@intel.com>
Message-Id: <20200910134851.7817-1-jin.yu@intel.com>
Acked-by: Raphael Norwitz <raphael.norwitz@nutanix.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>