2nd patch in series to update Cubic in conformation with RFC8312bis.
This updates the calculation of K using the formula from this RFC document.
The new formula additionally uses "cwnd_epoch" for calculating K.
(1st in series: D40436)
This Diff is sliced from a summary patch provided by VMware to improve short RTT performance of Cubic.
Once all patches have been prepared and reviewed, they will go in together to make an atomic change
to cubic from pre-RFC status, to 8312bis status.