Add firewalld support for Centos / Arch based systems

[squadramunter]

Should be nice if there is firewalld support using firewall-cmd command.

These are my firewall rules.

PostUp = firewall-cmd --zone=public --add-port 62156/udp && firewall-cmd --zone=public --add-masquerade
PostDown = firewall-cmd --zone=public --remove-port 62156/udp && firewall-cmd --zone=public --remove-masquerade

you could make a variable for the port that correspondent to the random generated port number in the script.

There is already a fwtype.txt and if I could change it to firewall-cmd it would be great for me.