ZAP_HASH_IDX
idx = ZAP_HASH_IDX(h, zap->zap_phys->zap_ptrtbl.zt_shift);
li = ZAP_HASH_IDX(ent->hash, prefixlen);
hi = ZAP_HASH_IDX(ent->hash, zt->zt_shift);
li = ZAP_HASH_IDX(ent->hash, prefixlen);