Make iptables firewall faster.
Make quantum-ovs-agent's periodic status reporting much faster.

Instead of querying ovs-vsctl for every port on br-int, we just dump the entire
interfaces table and grab what we need.

Pathological case will have poor behaviour: a host with few interfaces per
bridge but many many bridges. I'm not sure if quantum does this. AFAIK, there's
always one br-int and it's shared by tenants using vlans or GRE tunnels.