i40e: driver ethtool core

This patch contains the ethtool interface and implementation.

The goal in this patch series is minimal functionality while not
including much in the way of "set support."
Signed-off-by: NJesse Brandeburg <jesse.brandeburg@intel.com>
Signed-off-by: NShannon Nelson <shannon.nelson@intel.com>
CC: PJ Waskiewicz <peter.p.waskiewicz.jr@intel.com>
CC: e1000-devel@lists.sourceforge.net
Tested-by: NKavindya Deegala <kavindya.s.deegala@intel.com>
Signed-off-by: NJeff Kirsher <jeffrey.t.kirsher@intel.com>