mac80211: handle extended channel switch announcement

Handle the (public) extended channel switch announcement
action frames. Parts of the data in these frames isn't
really in IEs, but put it into the elems struct anyway
to simplify the handling.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>

diff --cc include/linux/ieee80211.h
Simple merge

diff --cc net/mac80211/mlme.c
Simple merge

diff --cc net/mac80211/rx.c
Simple merge