Inner protocol being UDP should not stop us from verifying Outer UDP
checksum correctness.

If the Outer protocol is not UDP (NVGRE) we should not be doing a UDP
checksum check. If the packet has zero checksum, skip checksum check.

Change-ID: Ie7f153feb276a59f66a54a0938901b2c0a8100fa
Signed-off-by: Anjali Singhai Jain <anjali.singhai@intel.com>
Tested-by: Jim Young <james.m.young@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>