Set admin portal to listen only on loopback

[hpux735]

6. Block your firewall on port 8080 to prevent unencrypted access to lorawan server from public internet. All interaction should be through encrypted 8443 port.
7. Restart nginx: sudo service nginx restart

This is a great primer, thanks for writing it. But there's one thing I've been looking for in the documentation, and that's how to set the 8080 port to only listen on the loopback address. The firewall will work, of course, but it would be better to also not listen on the external interface at all.

Originally posted by @hpux735 in https://github.com/gotthardp/lorawan-server/issues/386#issuecomment-995436077