vhost: fix virtqueue access check in vhost-user setup

Calling vring_invalidate must be done with a (write) lock taken on the
virtqueue.

Fixes: 72d002b ("vhost: fix vring address handling during live migration")
Cc: stable@dpdk.org

Signed-off-by: David Marchand <david.marchand@redhat.com>
Acked-by: Eelco Chaudron <echaudro@redhat.com>
Reviewed-by: Maxime Coquelin <maxime.coquelin@redhat.com>

lib/vhost/vhost_user.c

@@ -2198,7 +2198,9 @@ vhost_user_get_vring_base(struct virtio_net **pdev,
 
 	vhost_user_iotlb_flush_all(dev);
 
+	rte_rwlock_write_lock(&vq->access_lock);
 	vring_invalidate(dev, vq);
+	rte_rwlock_write_unlock(&vq->access_lock);
 
 	return RTE_VHOST_MSG_RESULT_REPLY;
 }