mac80211: make wake/stop_queue_by_reason() functions static

Fixes sparse warnings:

net/mac80211/util.c:355:6: warning: symbol
  'ieee80211_wake_queue_by_reason' was not declared. Should it be static?
net/mac80211/util.c:385:6: warning: symbol
  'ieee80211_stop_queue_by_reason' was not declared. Should it be static?

Thanks to Johannes Berg for reporting this.

Signed-off-by: Kalle Valo <kalle.valo@iki.fi>
Signed-off-by: John W. Linville <linville@tuxdriver.com>