iwlwifi: keep track of bt coex enable/disable stage

For debugging purpose, keep track of the bt coex enable/disable state.

Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>
diff --git a/drivers/net/wireless/iwlwifi/iwl-dev.h b/drivers/net/wireless/iwlwifi/iwl-dev.h
index 836f181..8dda678 100644
--- a/drivers/net/wireless/iwlwifi/iwl-dev.h
+++ b/drivers/net/wireless/iwlwifi/iwl-dev.h
@@ -1468,6 +1468,7 @@
 	};
 
 	/* bt coex */
+	u8 bt_enable_flag;
 	u8 bt_status;
 	u8 bt_traffic_load, last_bt_traffic_load;
 	bool bt_ch_announce;