I used Linux and are connected to internet through a wireless, portable wifi modem. I created a listen server with the 'Create' option in game to play with my friends. After entering the server, I check the server list again to found that my server isn't listed there! My friend can't see the server too. Previously I have copied the server.cfg on the 'server' directory to ~/.xonotic/data and renamed it as autoexec.cfg. I only set two variables on that file: `sv_public` to 1 and `hostname` to a hostname that I want. What's wrong?