mlx5e: Ensure rx timestamps are monotonically increasing

[gallatin]

Summary

The clock calibration routine currently can result in rx timestamps
jumping backwards, which can confuse the TCP stack.
Ensure they are monotonically increasing by estimating what
we'd calculate as the next timestamp and clamp the calibration
so new timestamps are no earlier in time.

[nickbanks_netflix.com]

Tested this out and it reduced the backward time jumps, as measured by TCP connections, by >99.98% (down from 73,800 to 10).