LinuxKPI: add KPI for netdev_notifier_info returning ifp

[bz]

Summary

While currently the ifp gets cast to a net_device and then returned
and consumers are expecting an ifp again allow parallel usage now and
in the future by extending and also passing the ifp directly back in
the netdev_notifier_info. Add a function to return the ifp instead of
the net_device.

Sponsored by: The FreeBSD Foundation
MFC after: 10 days
Suggested by: hselasky

Test Plan

Currently untested; not even compiled.

[• hselasky]

You may want to bump the __FreeBSD_version too, due to changing an existing API.

The change looks good to me.

--HPS