sendudp
return sendudp(d, pkt, len);
ssize_t sendudp(struct iodesc *, void *, size_t);
sendudp, send_head, send_tail - send_head,
res = sendrecv(h->iodesc, sendudp, &wbuf.t, wtail - (char *)&wbuf.t,
res = sendrecv(h->iodesc, sendudp, &wbuf.t, wtail - (char *)&wbuf.t,
(void)sendudp(h->iodesc, &wbuf.t, wtail - (char *)&wbuf.t);