[list] filter out unmanaged IPs

Say in:
```plain
$ multipass launch minikube
Launched: minikube

$ multipass list
Name State IPv4 Image
minikube Running 10.152.94.30 Ubuntu 20.04 LTS
172.17.0.1
192.168.49.1
```

Only the first IP is reachable from the outside, the other two are internal to the instance. We should filter out those interfaces we don't manage.

Reproduce the issue with `multipass launch minikube` followed by `multipass list`, and inspect the implementation of the `list` command and its instance-networking data. The change is done when `list` retains the externally reachable address while omitting the unmanaged internal addresses shown in the report.

Written by the indexing model from the issue text.