mac80211: clean up ieee80211_set_channel

There's no need for ieee80211_set_channel to check
whether a change in configuration happened since
ieee80211_hw_config() auto-detects it.

Additionally, it's wrong to pretend the HT config
for the BSS changed, it didn't, the BSS can't be
up & running (AP beaconing etc.) when the channel
type is changed anyway.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>