svc/conntrack.in: Contemplate multiple address families.
A number of relatively simple changes, with no overall functional change
except for a few diagnostic messages.
* Attach the address-family code and a name string to the
`InetAddress' class. This will mean that we can add new address
families without breaking things.
* Make `testaddrs' (and related variables) be a dictionary, mapping
address families to addresses, rather than just a lone address.
* Ensure that the networks in a peer assignment belong to the same
family. They will do for now, because there's only one.
* Have `kickpeers' maintain a local IP address for each family, rather
than just a single one.