ixgbe: disable LRO by default

This patch disables LRO by default in favor of GRO.

LRO is incompatible with forwarding and is disabled when forwarding
is turned on which makes the default offloads of the driver
inconsistent. LRO can still be enabled via ethtool.

Signed-off-by: Emil Tantilov <emil.s.tantilov@intel.com>
Tested-by: Darin Miller <darin.j.miller@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>