HN_TXD_FLAG_ONLIST
KASSERT((txd->flags & HN_TXD_FLAG_ONLIST) == 0,
txd->flags |= HN_TXD_FLAG_ONLIST;
(txd->flags & HN_TXD_FLAG_ONLIST) &&
txd->flags &= ~HN_TXD_FLAG_ONLIST;
txd->flags |= HN_TXD_FLAG_ONLIST;