How to enable Android Ip forwarding
This method worked for me, I just setup android as proxy server and need enable forwarding 

Use ROOT explorer and EDIT this file: /proc/sys/net/ipv4/ip_forward

add this syntax:

iptables -F -t filter

iptables -P FORWARD ACCEPT 


if that file not found, try install busybox first.. but I guess that file by default is available on android system.