iwlwifi: add option to disalbe LED

Led has no use for some platform.
Add additional module parameter option to disable LED

Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>
diff --git a/drivers/net/wireless/iwlwifi/iwl-agn.c b/drivers/net/wireless/iwlwifi/iwl-agn.c
index 3e429a3..90315c6 100644
--- a/drivers/net/wireless/iwlwifi/iwl-agn.c
+++ b/drivers/net/wireless/iwlwifi/iwl-agn.c
@@ -2097,7 +2097,7 @@
 
 module_param_named(led_mode, iwlagn_mod_params.led_mode, int, S_IRUGO);
 MODULE_PARM_DESC(led_mode, "0=system default, "
-		"1=On(RF On)/Off(RF Off), 2=blinking (default: 0)");
+		"1=On(RF On)/Off(RF Off), 2=blinking, 3=Off (default: 0)");
 
 module_param_named(power_save, iwlagn_mod_params.power_save,
 		bool, S_IRUGO);