LinuxKPI: add 802.11 compat code

Add 802.11 compat code for mac80211 and to a minimal degree cfg80211.
This allows us to compile and use basic functionality of wireless
drivers such as iwlwifi.

This is a constant work in progress but having it in the tree will
allow others to test and more easy to track changes and avoid having
snapshots no longer applying to branches.

Sponsored by: The FreeBSD Foundation
MFC after: 3 days