This PR started as an exploration of "using Max RTT as PTO". This exploration was inconclusive -- using the Max RTT "since the beginning of the connection" often fails, because the high RTT values observed during start up are not adequate values for the retransmission time in the "stable" phases. However, slightly diminishing the value of the timer by using 3 rttvar instead of 4 appears advantageous.
This PR started as an exploration of "using Max RTT as PTO". This exploration was inconclusive -- using the Max RTT "since the beginning of the connection" often fails, because the high RTT values observed during start up are not adequate values for the retransmission time in the "stable" phases. However, slightly diminishing the value of the timer by using 3 rttvar instead of 4 appears advantageous.