v_isolated
if (vp->v_isolated != 0) {
vp->v_isolated = v->v_secondary;
KASSERT(v->v_isolated == 0); /* vs NFIND should found this */
KASSERT(vp->v_isolated == v->v_secondary);
vp->v_isolated = 0;
ifbrpv->ifbrpv_secondary = vp->v_isolated;