should use OFGroups for multiple output

[anarkiwi]

Currently, the flood manager builds output action lists to implement VLAN flooding, one list for every ingress port, outputting to all ports except the ingress port (since it is incorrect to flood out the ingress port).

We should really use groups instead which would scale better (smaller action list, also group OFPGT_ALL automatically exclude outputting to ingress port so only one output entry is needed per VLAN - see https://www.opennetworking.org/images/stories/downloads/sdn-resources/onf-specifications/openflow/openflow-spec-v1.3.3.pdf section 5.7.1).

[anarkiwi]

7caab35