L2TP_SEQ_DIFF
if ((nack = L2TP_SEQ_DIFF(nr, seq->rack)) <= 0)
if (L2TP_SEQ_DIFF(nr, seq->ns) > 0) {
while ((i = L2TP_SEQ_DIFF(seq->ns, seq->rack)) < seq->cwnd
self_unack = L2TP_SEQ_DIFF(seq->nr, seq->xack);
peer_unack = L2TP_SEQ_DIFF(seq->ns, seq->rack);
if (L2TP_SEQ_DIFF(ns, seq->nr) <= 0)
&& L2TP_SEQ_DIFF(ns, hpriv->nr) < 0) {