mac80211: use oper_channel in utils and config

Using hw.conf.channel is wrong as it could be the
temporary channel if any function like the beacon
get function is called while scanning or during
other temporary out-of-channel activities.

Use oper_channel instead.

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

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

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

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