docker-ce: make docker-ce firewall handling configurable

Openwrt has a own firewall service called fw3, that supports firewall zones.
Docker can bypass the handling of the zone rules in openwrt via custom
tables. These are "always" processed before the openwrt firewall.
Which is prone to errors!

Since not everyone is aware that the firewall of openwrt will
not be passed. And this is a security problem because a mapped port is
visible on all interfaces and so also on the WAN side.
If the firewall handling in docker is switched off, then the port in
fw3 must be explicitly released and it cannot happen that the
port is accidentally exported to the outside world via the interfaces on
the WAN zone.

So all rules for the containers should and so must be made in fw3.

Signed-off-by: Florian Eckert <fe@dev.tdt.de>

utils/docker-ce/files/etc/config/dockerd

@@ -9,6 +9,7 @@ config globals 'globals'
 	option log_level "warn"
 	list hosts "unix:///var/run/docker.sock"
 	option bip "172.18.0.1/24"
+#	option iptables "0"
 #	list registry_mirrors "https://<my-docker-mirror-host>"
 #	list registry_mirrors "https://hub.docker.com"