Merge branch 'ipv6-gre-offloads'

Alexander Duyck says:

====================
Add support for offloads with IPv6 GRE tunnels

This patch series enables the use of segmentation and checksum offloads
with IPv6 based GRE tunnels.

In order to enable this series I had to make a change to
iptunnel_handle_offloads so that it would no longer free the skb.  This was
necessary as there were multiple paths in the IPv6 GRE code that required
the skb to still be present so it could be freed.  As it turned out I
believe this actually fixes a bug that was present in FOU/GUE based tunnels
anyway.

Below is a quick breakdown of the performance gains seen with a simple
netperf test passing traffic through a ip6gretap tunnel and then an i40e
interface:

Throughput Throughput  Local Local   Result
           Units       CPU   Service Tag
                       Util  Demand
                       %
3544.93    10^6bits/s  6.30  4.656   "before"
13081.75   10^6bits/s  3.75  0.752   "after"
====================

Signed-off-by: David S. Miller <davem@davemloft.net>