Documentation: use separate default metrics port

Documentation/op-guide/monitoring.md

@@ -5,7 +5,7 @@ Each etcd server exports metrics under the `/metrics` path on its client port.
 The metrics can be fetched with `curl`:
 
 ```sh
-$ curl -L http://localhost:2379/metrics | grep -v debugging # ignore unstable debugging metrics
+$ curl -L http://localhost:9379/metrics | grep -v debugging # ignore unstable debugging metrics
 
 # HELP etcd_disk_backend_commit_duration_seconds The latency distributions of commit called by backend.
 # TYPE etcd_disk_backend_commit_duration_seconds histogram