i40e: Allow RSS Hash set with less than four parameters

This patch implements a feature change which allows using ethtool to set
RSS hash opts using less than four parameters if desired.

Change-ID: I0fbb91255d81e997c456697c21ac39cc9754821b
Signed-off-by: Carolyn Wyborny <carolyn.wyborny@intel.com>
Signed-off-by: Kiran Patil <kiran.patil@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>