interfaces: T3871: never rename an interface which is in use

Editing the map and then plugging any card in applied the edit to every
interface at once, because the pass re-resolves the whole system whatever
woke it. A running port was renamed out from under the configuration still
naming it, a bridge member included since members became discoverable.

Leave a name alone while the system is relying on it - the port is up, or it
has a master. At boot that is true of nothing, as the pass runs before the
configuration is applied, so naming is unaffected; afterwards it is true of
everything configured, and a card which has just arrived is still down. Say
in the log and the status file when a rename was refused, as the map and the
running system then disagree until the next boot.

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