* Document fmt_addr_impl() and friends.
* Parenthesize macro arguments.
* Rename get_first_listener_addrport_for_pt() to
  get_first_listener_addrport_string().
* Handle port_cfg_t with no_listen.
* Handle failure of router_get_active_listener_port_by_type().
* Add an XXX to router_get_active_listener_port_by_type().