Update the Firewall Policy

Set the firewall policy appropriate for the TCP port that's used by Tang.
- If you're using the default port, you can run:
```
sudo firewall-cmd --add-service=http
```
- If you aren't using the default port for the Tang server and have configured the server to run on a specified port number, such as port 7500, run:
```
sudo firewall-cmd --add-port=7500/tcp
```

Make the firewall policy permanent.

sudo firewall-cmd --runtime-to-permanent

If you haven't already started the Systemd socket, do this so that the Tang service can run on the configured port. See Start and Enable the Systemd Tang Socket for more information.