Move per-container forward rules to DOCKER chain

Closes #6034

Docker-DCO-1.1-Signed-off-by: Ian Bishop <ianbishop@pace7.com> (github: porjo)
sudo echo redirect cannot work as the redirection is done in scope of the uid of the user executing sudo.
You can use tee instead:
    $ echo 1 | sudo tee /proc/sys/net/ipv4/ip_forward
Regards