As D4294 appears to be abandoned, reviving the particular aspect
of delayed Acknowledgments here, as a single change.
It seems that a few other stacks have been moving to shorter delayed
ack timeout intervals of around 40 to 50ms. Given that precedent,
it appears prudent to reduce arificial delay introduced to some
request-response workload, by following their example.
One of the problems addressed with rtt_slope in my expirience is
the unpredictability, if the remote host is using delayed acks, and
when, what the timeout is. To err on the save side, i tended to
keep rto_slop to 2* delack...
Making the actual minimum allowed RTO 3 ticks requires different
changes than those proposed in D4294 (only the default minimum is
touched that way, not made sure that minRTO is at least 3 ticks.)