iwlwifi: move HT configuration data into context

A lot of HT configuration semantically belongs into
the context, even if right now it will never be
different between contexts. Move it so we're better
prepared for future changes in mac80211.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>