e1000: configure and read MDI settings

This is the implementation in e1000 to allow ethtool to force
MDI state, allowing users to work around some improperly
behaving switches.

Forcing in this driver is for now only allowed when auto-neg is enabled.

To use must have the matching version of ethtool app that supports
this functionality.

Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
CC: Tushar Dave <tushar.n.dave@intel.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>