SOULFRAME USES UDP PORTS 4960 AND 4965 & THE TCP PORT RANGE 6695 - 6699 (or whichever ports are set at the in-game options). Your router needs to let traffic on those ports through to your PC. For your convenience, these ports and your local IP address are shown in the network analysis dialog.
The instructions for forwarding ports on your router vary by manufacturer and model; please consult your router's manufacturer's support site or your internet service provider for details on how to correctly forward these ports to your PC.