udp: Add support for software checksum and GSO_PARTIAL with GSO offload

This patch adds support for a software provided checksum and GSO_PARTIAL
segmentation support. With this we can offload UDP segmentation on devices
that only have partial support for tunnels.

Since we are no longer needing the hardware checksum we can drop the checks
in the segmentation code that were verifying if it was present.

Change-Id: I7a24452f0f906e391fb968c3bac58177dd6c407d
CRs-Fixed: 2351793
Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Acked-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Git-commit: 6053d0f189064302420930f9ef9022e24a04946a
Git-repo: https://git.kernel.org/pub/scm/linux/kernel/git/davem/net.git


Signed-off-by: Sean Tranchetti <stranche@codeaurora.org>