The patch:

commit 15e473046cb6e5d18a4d0057e61d76315230382b
Author: Eric W. Biederman <ebiederm@xmission.com>
Date:   Fri Sep 7 20:12:54 2012 +0000

    netlink: Rename pid to portid to avoid confusion
    
    It is a frequent mistake to confuse the netlink port identifier with a
    process identifier.  Try to reduce this confusion by renaming fields
    that hold port identifiers portid instead of pid.
    
    I have carefully avoided changing the structures exported to
    userspace to avoid changing the userspace API.
    
    I have successfully built an allyesconfig kernel with this change.
    
    Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
    Acked-by: Stephen Hemminger <shemminger@vyatta.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>

Changed the struct members:

struct netlink_notify->pid    to
struct netlink_notify->portid

struct genl_info->snd_pid     to
struct genl_info->snd_portid

To help backport this and not have to #ifdef around it against
kernel versions compat has introduced two helpers for us to
simply do the backport with two macro helpers:

genl_info_snd_portid()
netlink_notify_portid()

This takes care of the work for us requiring only one
single line change. If we get another patch thrown into
this file then I suspect we can extract SMPL out of it
and use it to backport further collateral evolutions like
this one should other drivers / subsystem need this change.