You don't need any extra rate limiting iptables rules in combination with libcod's builtin rate limiting.
I don't know which new features you are using from damage99's libcod branch.
But It isn't protected against SV_DirectConnect flooding.
https://github.com/voron00/libcod/co...42a88d9cf09ac9
The most up-to-date fork is https://github.com/voron00/libcod