ixgbe: Add support for VXLAN RX offloads

Add support for VXLAN RX offloads for the X55x devices that support
them.

Signed-off-by: Mark Rustad <mark.d.rustad@intel.com>
Tested-by: Phil Schmitt <phillip.j.schmitt@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>