iwlwifi: eliminate conf_ht

This patch eliminates the use of conf_ht in iwlwifi driver, replacing it
with bss_info_changed.

Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: Ron Rindjunsky <ron.rindjunsky@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>