pf_unit2idx
KASSERT(pf_unit2idx(unit) < nitems(pf_tcount));
if (pf_tcount[pf_unit2idx(unit)] >= (PF_ANCHOR_STACK_MAX * 8))
pf_tcount[pf_unit2idx(unit)]++;
KASSERT(pf_unit2idx(t->pft_unit) < nitems(pf_tcount));
KASSERT(pf_tcount[pf_unit2idx(t->pft_unit)] >= 1);
pf_tcount[pf_unit2idx(t->pft_unit)]--;