config: MetricsPort seems to keep wanting to open

Several users have reported this problem and I just stumble on it by enabling MetricsPort on a relay:

Apr 15 14:16:56.005 [notice] Opening Metrics listener on 127.0.0.1:9090                                                                                                        
Apr 15 14:16:56.005 [notice] Opened Metrics listener connection (ready) on 127.0.0.1:9090
[...]
Apr 15 14:17:00.370 [notice] Opening Metrics listener on 127.0.0.1:9090                                                           
Apr 15 14:17:00.370 [warn] Could not bind to 127.0.0.1:9090: Address already in use. Is Tor already running?
Apr 15 14:18:00.375 [notice] Opening Metrics listener on 127.0.0.1:9090                                                                                                        
Apr 15 14:18:00.375 [warn] Could not bind to 127.0.0.1:9090: Address already in use. Is Tor already running?
...

The port works and is open but every minute, Tor seems to retry to open it. Possible backport candidate.