mac80211: clean up channel type config

The channel_type really doesn't need to be the only member in
a new structure, so remove the struct. Additionally, remove
the _CONF_CHANGE_HT flag and use _CONF_CHANGE_CHANNEL when the
channel type changes, since that's enough of a change to require
reprogramming the hardware anyway.

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