iwlwifi: add debugfs to control stuck queue timer

In current implementation, stuck queue timer is fixed to 1 second. Add
debugfs file to modify the timer to enhance the flexibility:

Set the monitor_period as following:
   0: disable stuck queue force reset function
   1 - 60000: monitor period (1 - 60 second)

Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/drivers/net/wireless/iwlwifi/iwl-dev.h b/drivers/net/wireless/iwlwifi/iwl-dev.h
index 7a96d9d..bb92a7f 100644
--- a/drivers/net/wireless/iwlwifi/iwl-dev.h
+++ b/drivers/net/wireless/iwlwifi/iwl-dev.h
@@ -1064,6 +1064,7 @@
 #define IWL_DEF_MONITORING_PERIOD	(1000)
 #define IWL_LONG_MONITORING_PERIOD	(5000)
 #define IWL_ONE_HUNDRED_MSECS   (100)
+#define IWL_MAX_MONITORING_PERIOD	(60000)
 
 /* BT Antenna Coupling Threshold (dB) */
 #define IWL_BT_ANTENNA_COUPLING_THRESHOLD	(35)