Enabled TCP fast open as the container runs on debian.
Cleared the forwarding secret, security measure.
Renamed forwarding mode to LEGACY so users don't get the initial startup error, and would work out of the box.
I'm proposing this change as it will add an Environment Variable used by the EXILED (a Popular SCP:SL Mods Framework) to run its auto updater. Otherwise, the user could run into an issue with his server not starting.
I know this is normally not used to support modifications. But as this is only an environment variable I will propose the change anyway.