ixgbe: add LRO support

Support for in-kernel LRO with the ability to enable/disable via ethtool
based on comments from Ben Hutchings.

Signed-off-by: Mallikarjuna R Chilakala <mallikarjuna.chilakala@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: PJ Waskiewicz <peter.p.waskiewicz.jr@intel.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>