Import a netdevice update complementing the last remaining bits of
the old ifnet derived implementation. Along add a (for now) task
based NAPI implementation.

This is the minimal set of chnages which are needed for the initial
import of wireless drivers. The NAPI implementation has an option to
still switch to "direct dispatch" as it had been used by these drivers
before not relying on a deferred context along with some printf tracing.
This has been helpful in the last weeks with debugging and will be
cleaned once we have had broader testing and are sure this is fine as-is.
Should we need a more time-sensitive or load-sensitive response
in the future we can always switch to something more sophisticated.

More netdevice changes will come eventually for further drivers
and some XXX [TODO] marks are left in place.

Sponsored by: The FreeBSD Foundation
MFC after: 10 days