i40e: rename 'cmd' variables in ethtool interface

After the switch to the new ethtool API, ethtool passes us
ethtool_ksettings structs instead of ethtool_command structs, however we
were still referring to them as 'cmd' variables.  This renames them to
'ks' variables which makes the code easier to understand.

Signed-off-by: Alan Brady <alan.brady@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>