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>

drivers/net/wireless/iwlwifi/iwl-tx.c

@@ -728,7 +728,7 @@ int iwl_tx_skb(struct iwl_priv *priv, struct sk_buff *skb)
 
 	/* drop all data frame if we are not associated */
 	if (ieee80211_is_data(fc) &&
-	    (priv->iw_mode != NL80211_IFTYPE_MONITOR ||
+	    (!iwl_is_monitor_mode(priv) ||
 	    !(info->flags & IEEE80211_TX_CTL_INJECTED)) && /* packet injection */
 	    (!iwl_is_associated(priv) ||
 	     ((priv->iw_mode == NL80211_IFTYPE_STATION) && !priv->assoc_id) ||