upstream: the messaging layer between sshd-session and sshd-auth had a

upstream: the messaging layer between sshd-session and sshd-auth had a

maximum message size of 256KB. Some people apparently have configurations
larger than this and would hit this limit.

Worse, there was no good logging that could help diagnose what was
going wrong.

So this bumps the maximum message size to 4MB and implements an early
check (usable via the sshd -t test mode) that will report it to the
user where it is hopefully more visible.

bz3808, reported by Dmitry Belyavskiy, ok dtucker@

OpenBSD-Commit-ID: 69c303fb68cbd1a4735936835d67a71e7b57f63b