bbf: add support anywan type upstream iface in igmp
It was observed on dg400prime that the uci config was not correctly generated when wan was of type anywan, this has been taken care of in this patch. For anywan type IP interface, the list of upstream interfaces is generated to keep each interface in mind. So, Device.IP.Interface.2 in this case will generate list upstream_interface 'eth5.1' list upstream_interface 'atm0.1' list upstream_interface 'ptm0.1'
test:
- Verify that config is correctly generated for normal interface.
- Verify that config is correctly generated for anywan interface.
- Verify that config is correctly generated for bridge interface.