[systemd-devel] networkd: ip forwarding fixes

[Benedikt Morbach]

After some more testing/thinking yesterday, I've decided to split this up and
only do the bugfix for now. At least on my machine the global ip_forward setting
is not needed, as long as all relevant interfaces have forwarding enabled.

I still dislike that the default for networkd managed interfaces does not
necessarily match the default for everything else.  I think it would be better
if networkd honored ip_forward=1 if set and let the user disable it on
individual interfaces via IPForward=no. But that is unrelated 

Added in a small fix to the docs for good measure.

Greetings
Benedikt