ixgbe: check for 128-bit authentication

Make sure the Security Association is using
a 128-bit authentication, since that's the only
size that the hardware offload supports.

Signed-off-by: Shannon Nelson <shannon.nelson@oracle.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>