Actually ensure IPv6 forwarding is disabled
Actually ensure IPv6 forwarding is disabled

There is no net.ipv6.ip_forward parameter at all! The correct parameter
to use is net.ipv6.conf.all.forwarding.

Luckily, IPv6 forwarding is disabled by default at the kernel level.
systemd-networkd doesn't automatically enable it; Debian 8, Fedora 23,
and Arch don't seem to either.

Also closes #14

adrelanos/corridor,rustybird/corridor