nexthop_ref
struct nexthop *nexthop_ref(struct nexthop *);
a->nexthop = nexthop_ref(nexthop);
state->nexthop = nexthop_ref(nh);
p->nexthop = nexthop_ref(nexthop);
*nexthop = nexthop_ref(setnh);
nexthop_ref(nh); /* take reference for lookup */
return nexthop_ref(nh);