igmpproxy: fix creation of firewall rules

igmpproxy: fix creation of firewall rules

The init sccript for igmpproxy uses the option 'network' both as an interface name for fetching the l3_device name and for creating the firewall rules. This only works if the name of the network and firewall zone are identical.

This commit introduces a new option 'zone' for configuring the upstream and downstream firewall zones in order for the init script to create the required firewall rules automatically. When no such options are given, the init script falls back to not creating the firewall rules and the user can opt to create these manually.

Signed-off-by: Jaap Buurman <jaapbuurman@gmail.com>