cfg80211: export interface stopping function

This exports a new cfg80211_stop_iface() function.

This is intended for driver internal interface
combination management and channel switching.

Due to locking issues (it re-enters driver) the
call is asynchronous and uses cfg80211 event
list/worker.

Signed-off-by: Michal Kazior <michal.kazior@tieto.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

diff --cc include/net/cfg80211.h
Simple merge

diff --cc net/wireless/ap.c
Simple merge

diff --cc net/wireless/core.c
Simple merge

diff --cc net/wireless/core.h
Simple merge

diff --cc net/wireless/mesh.c
Simple merge

diff --cc net/wireless/trace.h
Simple merge

diff --cc net/wireless/util.c
Simple merge