[inetstack] Retransmission Timeout Calculator uses Floating Point

[BrianZill]

Back in olden times, when dinosaurs roamed the earth and floating-point units were on a separate processor board (e.g., VAX 750), TCP/IP stacks did all of their retransmission timeout calculations using integer arithmetic, as it was significantly faster than using floating point. Our current implementation uses floating-point.

We should review whether this is a performance problem or not.