iwlwifi: adding interrupt counter in debugfs for debugging

This patch adds interrupt statistics report to debugfs, this can help to
understand number of interrupts happened which including HW/SW error for
easier and better debugging.

in /sys/kernel/debug/ieee80211/phyN/iwlagn/data directory
use "cat interrupt" to view the current interrupt counter
use "echo 0 > interrupt" to clear interrupt counter

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 65d1a7f..db06980 100644
--- a/drivers/net/wireless/iwlwifi/iwl-debug.h
+++ b/drivers/net/wireless/iwlwifi/iwl-debug.h
@@ -75,6 +75,7 @@
 		struct dentry *file_log_event;
 		struct dentry *file_channels;
 		struct dentry *file_status;
+		struct dentry *file_interrupt;
 	} dbgfs_data_files;
 	struct dir_rf_files {
 		struct dentry *file_disable_sensitivity;