LinuxKPI: 802.11: basic implementation of *queue(s)/*txq*

Very basic implementations of ieee80211_{wake,stop}_queue[s],
as well as ieee80211_txq_schedule_start(), ieee80211_next_txq(),
and ieee80211_schedule_txq().
Various combinations of these are used by different wireless
drivers, incl. iwlwifi.

Sponsored by: The FreeBSD Foundation (parts of this work)
MFC after: 3 days