iwlagn: add bluetooth stats to debugfs

For WiFi/BT combo devices, add bluetooth statistics counter
read function to debugfs.

Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>
diff --git a/drivers/net/wireless/iwlwifi/iwl-core.h b/drivers/net/wireless/iwlwifi/iwl-core.h
index 2954a52..b60cf45 100644
--- a/drivers/net/wireless/iwlwifi/iwl-core.h
+++ b/drivers/net/wireless/iwlwifi/iwl-core.h
@@ -125,6 +125,8 @@
 				 size_t count, loff_t *ppos);
 	ssize_t (*general_stats_read)(struct file *file, char __user *user_buf,
 				      size_t count, loff_t *ppos);
+	ssize_t (*bt_stats_read)(struct file *file, char __user *user_buf,
+				 size_t count, loff_t *ppos);
 };
 
 struct iwl_temp_ops {