Use DHCP for all ethernet interfaces

Change the interface match of systemd-networkd from eth0 to eth* to match all local ethernet interfaces. This is particularly useful for Vagrant, as it requires two interfaces (one solely used for managing the machine, another e.g. for outbound connections) and for machines in general, as depending on their context (e.g. plain libvirt) the user may attach more interfaces and having DHCP available for them out-of-the-box is a quality of life improvement (as we do not know what the user intends to do with eth0 by default).