Flint: Port forwarding does no longer work when a VPN client is enabled on the router

[foxbazo]

@hansome To make sure I understand properly the instructions before applying them, can you confirm the following commands:
opkg update
opkg install iptables-mod-conntrack-extra
/etc/init.d/firewall restart

Then in case I have an issue, I can rollback typing this:
remove iptables-mod-conntrack-extra;
/etc/init.d/firewall restart

Is that correct?