Comment 5 for bug 1785816

There's some extra code that's added universally, and more code if a PHY which supports timestamping is present (currently only the DP83640 PHYTER device looks to be enabled by this option). What's done in the PHY-specific code depends on whether or not timestamping is enabled. So it's not completely a noop, but it's entirely possible that the real world impact in most cases will be negligible.