iwlwifi: debugFs to enable/disable HT40 support

Add debugfs file to enable/disable HT40(40MHz) channel support.
By default, 40MHz is supported if AP can support the function.

By echo "1" to "disable_ht40" file, iwlwifi driver will disable the
40MHz support and only allow 20MHz channel.

Because the information exchange happen during association time,
so enable/disable ht40 channel only can be performed when it is not
associated with AP.

Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/drivers/net/wireless/iwlwifi/iwl-debug.h b/drivers/net/wireless/iwlwifi/iwl-debug.h
index 609a681..fbe1776 100644
--- a/drivers/net/wireless/iwlwifi/iwl-debug.h
+++ b/drivers/net/wireless/iwlwifi/iwl-debug.h
@@ -88,6 +88,7 @@
 #ifdef CONFIG_IWLWIFI_LEDS
 		struct dentry *file_led;
 #endif
+		struct dentry *file_disable_ht40;
 	} dbgfs_data_files;
 	struct dir_rf_files {
 		struct dentry *file_disable_sensitivity;