TXDONE_BY_POLL
if (chan->txdone_method == TXDONE_BY_POLL && cl->knows_txdone)
chan->txdone_method = TXDONE_BY_POLL;
txdone = TXDONE_BY_POLL;
if (txdone == TXDONE_BY_POLL) {
if (!err && (chan->txdone_method & TXDONE_BY_POLL)) {