After introduction offer-delay accel-ppp stopped to answer NAK for REQUESTs if requested session is not existing
to give chance other servers to reply. But this causes that some broken clients enter to infinite REQUEST loop.
This patch corrects this issue, so if offer-delay is not configured (means that this is only server in the net) or
after receiving few REQUESTs accel-ppp send NAK for non-existing sessions.