SYN Flood Mitigation with synsanity

Introduced synsanity, an iptables module for Linux 3.x, to mitigate SYN flood attacks. synsanity generates SYN cookies outside the LISTEN socket lock, enabling multi-processor utilization during attacks. It validates the ACK packet and then allows it through to the standard Linux SYN cookie code, without touching subsequent packets. This avoids the need for a custom kernel and allows for maintenance of existing, patched kernels. The module is open-sourced.