iSo in doing final checks on OCA firmware with all the latest tweaks the dup-ack checking
packet drill script was failing with a number of unexpected acks. So it turns
out if you have the default recvwin set up to 1Meg (like OCA's do) and you
have no window scaling (like the dupack checking code) then we have another
case where we are always trying to update the rwnd and sending an
ack when we should not.

Sponsored by: Netflix Inc.
Differential Revision: https://reviews.freebsd.org/D25298