OFED: migrate LinuxKPI net_device/ifnet macros into ofed

The LinuxKPI net_device actually is an ifnet; in order to further
clean that up so we can extend "net_device" migrate the few macros
left into ofed and make sure the header is included in all files
which need access to the macros.

Sponsored by: The FreeBSD Foundation
MFC after: 12 days
Reviewed by: kib
Differential Revision: https://reviews.freebsd.org/D30477