upstream: Enforce maximum packet/block limit during

upstream: Enforce maximum packet/block limit during

pre-authentication phase

OpenSSH doesn't support rekeying before authentication completes to
minimise pre-auth attack surface.

Given LoginGraceTime, MaxAuthTries and strict KEX, it would be
difficult to send enough data or packets before authentication
completes to reach a point where rekeying is required, but we'd
prefer it to be completely impossible.

So this applies the default volume/packet rekeying limits to the
pre-auth phase. If these limits are exceeded the connection will
simply be closed.

ok dtucker markus

OpenBSD-Commit-ID: 70415098db739058006e4ebd1630b6bae8cc8bf6