xen-netback: re-import canonical netif header

The canonical netif header (in the Xen source repo) and the Linux variant
have diverged significantly. Recently much documentation has been added to
the canonical header which is highly useful for developers making
modifications to either xen-netfront or xen-netback. This patch therefore
re-imports the canonical header in its entirity.

To maintain compatibility and some style consistency with the old Linux
variant, the header was stripped of its emacs boilerplate, and
post-processed and copied into place with the following commands:

ed -s netif.h << EOF
H
,s/NETTXF_/XEN_NETTXF_/g
,s/NETRXF_/XEN_NETRXF_/g
,s/NETIF_/XEN_NETIF_/g
,s/XEN_XEN_/XEN_/g
,s/netif/xen_netif/g
,s/xen_xen_/xen_/g
,s/^typedef.*$//g
,s/^    /${TAB}/g
w
$
w
EOF

indent --line-length 80 --linux-style netif.h \
-o include/xen/interface/io/netif.h

Signed-off-by: Paul Durrant <paul.durrant@citrix.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: David Vrabel <david.vrabel@citrix.com>
Cc: Wei Liu <wei.liu2@citrix.com>
Acked-by: Wei Liu <wei.liu2@citrix.com>
Signed-off-by: David S. Miller <davem@davemloft.net>