vhost-user: add a migration blocker If VHOST_USER_PROTOCOL_F_LOG_SHMFD is not announced, block vhost-user migration. The blocker is removed in vhost_dev_cleanup(). Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com> Reviewed-by: Michael S. Tsirkin <mst@redhat.com> Signed-off-by: Michael S. Tsirkin <mst@redhat.com> Tested-by: Thibaut Collet <thibaut.collet@6wind.com>