LinuxKPI/OFED: (re)move inetdevice.h implementation

The two functions in linux/inetdevice.h are highly FreeBSD/ifnet
specific. This is a result of struct net_device being mapped to
struct ifnet.

The only known consumer of these functions are two files in the
ofed/infiniband code.

As a first step of cleaning up copy linux/inetdevice.h to
rdma/ib_addr_freebsd.h. (It stayed a separate file to preserve
copyright and license of the original file; otherwise it could be
merged into ib_addr.h where more EPOCH/vnet/.. are already used).

Slightly rename the function to not conflict with LinuxKPI
in the future.

Remove the three last, now unneeded includes of inetdevice.h and
zap linux/inetdevice.h to an empty header file with only the forward
include to netdevice.h remaining.

Sponsored-by: The FreeBSD Foundation
MFC-after: 2 weeks
Reviewed-by: hselasky, kib
X-D-R: D29366 (extracted as further cleanup)
Differential Revision: https://reviews.freebsd.org/D29434