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

LinuxKPI: 802.11: basic implementation of *queue(s)/*txq*
LinuxKPI: 802.11: deal with stopped queues

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.

Following 5a9a0d7803382321b5f9fff1deae5fb08463cf1a initialize the
queue values explicitly and deal with a stopped queue in
ieee80211_tx_dequeue().

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

(cherry picked from commit 5a9a0d7803382321b5f9fff1deae5fb08463cf1a)
(cherry picked from commit 0cbcfa1964de89cd346ee6f79437c6ab83a3b716)