Cleanup network interfaces

If boundary completes with an error or boundary process is killed, it doesn't make proper cleanup, and then user has to manually run:
```bash
ip link show
ip -o link show | awk -F': ' '{print $2}' | grep '^veth_h' | cut -d'@' -f1 | xargs -r -n1 sudo ip link delete
```

We should make sure clean up is always executed (network interfaces are removed, iptables rules are removed).
Consider running cleanup on startup? Consider adding cleanup command.

`UPD`: for some reason I wasn't able to reproduce this anymore. Even after sending SIGKILL to boundary process, `veth-pair` is deleted.
- [ ] Stale IPTables rules aren't cleaned up in such case, but it has much lower priority.
- [ ] `sysctl -w net.ipv4.conf.all.route_localnet=1` is also an issue, but has lower priority