iwlwifi: clean up unused NL80211_IFTYPE_MONITOR for Monitor mode

This patch clean up the code for NL80211_IFTYPE_MONITOR mode,
priv->iw_mode is set in add_interface, but add_interface is never called
for monitor mode.
The only way mac80211 informs us about monitor mode is through
configuring filter; since iw_mode will never set to
NL80211_IFTYPE_MONITOR, modify and remove all the code refer to
NL80211_IFTYPE_MONITOR and replace with iwl_is_monitor_mode() function
call.

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-scan.c b/drivers/net/wireless/iwlwifi/iwl-scan.c
index 25311e1c..799f5eb 100644
--- a/drivers/net/wireless/iwlwifi/iwl-scan.c
+++ b/drivers/net/wireless/iwlwifi/iwl-scan.c
@@ -747,7 +747,7 @@
 
 	scan->tx_cmd.len = cpu_to_le16(cmd_len);
 
-	if (priv->iw_mode == NL80211_IFTYPE_MONITOR)
+	if (iwl_is_monitor_mode(priv))
 		scan->filter_flags = RXON_FILTER_PROMISC_MSK;
 
 	scan->filter_flags |= (RXON_FILTER_ACCEPT_GRP_MSK |