Update Circuit.addresses to enumerate addresses of all child interfaces

[jathanism]

Depends on #260

If two interfaces bound to a circuit have child interfaces, Circuit.addresses should enumerate the child interfaces and return ALL addresses assigned to those interfaces.

Use-case example being an ae0 interface on either side w/ a child interface of ae0.0 where the addresses are assigned. We'd like to be able to account for both stub and sub-interface addressing.