from the interfaces table (and interface_state). The only place we will
store that is the wires table. When looking up an interface, we were
already loading the wires table, so we can still ask the interface for
its card and port, *if* it is wired up. And if it is not wired up,
asking the interface for anything related to the wire is nonsensical, so
print a backtrace and return an error.

Work in progress.