readudp
n = readudp(d, pkt, len, tleft);
ssize_t readudp(struct iodesc *, void *, size_t, time_t);
n = readudp(d, pkt, len, tleft);
while ((tmp_len = readudp(d, pkt, max_len, tleft)) > 0) {
len = readudp(d, pkt, max_len, tleft);