The current implementation of loss recovery algorithms SACK and NewReno are in
the same file(snd.go). The functions have multiple checks to see which one is
currently used by the endpoint. This CL will refactor and separate the
implementation of existing recovery algorithms which will help us to implement
new recovery algorithms(such as RACK) with less changes to the existing code.
There is no change in the behavior.
PiperOrigin-RevId: 342312166