LinuxKPI: netdevice.h remove more ifnet operating macros

Now that mlx4 and ofed either are operating on ifnet functions
directly or have a private copy of these macros, we can remove them
from linux/netdevice.h.
With this only the #define for net_device to ifnet is left.

Sponsored by: The FreeBSD Foundation
MFC after: 12 days
Reviewed by: kib
Differential Revision: https://reviews.freebsd.org/D30478