If there are v4 or v6 specific options we can keep those in separate sections,
but for the common options, we will use only one.
Moreovere only use DHCP=[yes/both|no/none|v4|v6] to enable or disable the clients.
When starting systemd-nspawn with --network-veth, we create a veth device called
host0 in the guest. Pick up on this and start a dhcp client on it. We will also
pick up host0 netdevs created by other containers should they chose to use the
same name.
Tom Gundersen