i40e/i40evf: Move Tx checksum closer to TSO

On all of the other Intel drivers we place checksum close to TSO as they
have a significant amount in common and it can help to reduce the decision
tree for how to handle the frame as the first check in TSO is to see if
checksumming is offloaded, and if it is not we can skip _BOTH_ TSO and Tx
checksum offload based on a single check.

Signed-off-by: Alexander Duyck <aduyck@mirantis.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>