make csf work on openvz host node

add this to /etc/csf/csfpre.sh

/sbin/iptables -A INPUT -i venet0 -j ACCEPT

/sbin/iptables -A OUTPUT -o venet0 -j ACCEPT

/sbin/iptables -A FORWARD -j ACCEPT -p all -s 0/0 -i venet0

/sbin/iptables -A FORWARD -j ACCEPT -p all -s 0/0 -o venet0