RFC Local checksum offload for VXLAN

When the inner packet checksum is offloaded, the outer UDP checksum is easy
to calculate as it doesn't depend on the payload (because the inner checksum cancels out everything from the inner packet except the pseudo header).
Thus, transmit checksums for VXLAN (and in principle other encapsulations,
but I haven't enabled it for / tested with those) can be offloaded on any device supporting NETIF_F_HW_CSUM. Only the innermost checksum has to be offloaded, the rest are filled in by the stack.
Tested by hacking a driver to report NETIF_F_HW_CSUM, call skb_checksum_help
before transmitting a packet, and not actually offload anything to the hw. I did it that way because I don't have any hw that can actually offload the inner checksum; but I should be able to get hold of some soon.

Edward Cree (2):
net: udp: local checksum offload for encapsulation
net: vxlan: enable local checksum offload on HW_CSUM devices

 drivers/net/vxlan.c |  5 ++++-
 net/ipv4/udp.c      | 31 +++++++++++++++++++++++++++----
 2 files changed, 31 insertions(+), 5 deletions(-)

2.4.3