readether
n = readether(d, pkt, len, tleft, &etype);
n = readether(d, ip, len + sizeof(*ip), tleft, &etype);
ssize_t readether(struct iodesc *, void *, size_t, saseconds_t, u_int16_t *);
n = readether(d, pkt, len, tleft, &etype);