nat_keepalive_work
struct delayed_work nat_keepalive_work;
net = container_of(work, struct net, xfrm.nat_keepalive_work.work);
schedule_delayed_work(&net->xfrm.nat_keepalive_work,
schedule_delayed_work(&net->xfrm.nat_keepalive_work, 0);
INIT_DELAYED_WORK(&net->xfrm.nat_keepalive_work, nat_keepalive_work);
disable_delayed_work_sync(&net->xfrm.nat_keepalive_work);