collectd: add iptables uci config

Signed-off-by: Florian Eckert <fe@dev.tdt.de>
(cherry-picked for 19.07)
Signed-off-by: Hannu Nyman <hannu.nyman@iki.fi>

utils/collectd/files/collectd.uci

@@ -81,6 +81,15 @@ config globals 'globals'
 #	list Interface 'br-lan'
 #	option IgnoreSelected '0'
 
+#config plugin 'iptables'
+#	option enable '1'
+
+#config iptables_match
+#	option table 'nat'
+#	option chain 'zone_wan_postrouting'
+#	option index '1'
+#	option name 'WLAN-Clients traffic'
+
 #config plugin 'irq'
 #	option enable '0'
 #	list Irq '2'