tcp: Update cubic CC module variable names to align with RFC8312bis

[rscheff]

Summary

This is the first patch in a series of patches, to update the FBSD
cubic CC module to better align with cubic as specified in RFC8312bis.

• Renamed a few cubic state variables to the variable names found in

the RFC8312bis specification. This makes the code more understandable
for someone reading the RFC and the code. It also makes the variable
naming convention more uniform.

This diff was extracted from a patch by Bhaskar Pardeshi at VMware Inc.

No functional change.

[tuexen]

I think you are not only renaming variables, but also adding new ones. Please reflect that in the commit message.

[cc]

Is this patch targeted at FreeBSD15 head, after FreeBSD 14 is branched? Is this patch just for early review and is not planned to commit until FreeBSD 15 becomes the head?