Merge branch 'xen_netback'

xen-netback: IPv6 offload support

====================
This patch series adds support for checksum and large packet offloads
into xen-netback.  Testing has mainly been done using the Microsoft
network hardware certification suite running in Server 2008R2 VMs with
Citrix PV frontends.

v2:
- Fixed Wei's email address in Cc lines

v3:
- Responded to Wei's comments:
 - netif.h now updated with comments and a definition of
   XEN_NETIF_GSO_TYPE_NONE.
 - limited number of pullups
- Responded to Annie's comments:
 - New GSO_BIT macro

v4:
- Responded to more of Wei's comments
- Remove parsing of IPv6 fragment header and added warning

v5:
- Added comment concerning the value chosen for PKT_PROT_LEN
- Dropped deprecation of feature-no-csum-offload
====================

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