The systemd 209 release is a major release that brings many new features, including a new systemd-networkd component for configuring and bringing up your network. It appears that in systemd there isn't an easy way to disable this feature if you don't want it: it's enabled by default and instead of issuing a command to disable it, it needs to be hard-masked out of the service file.
A Phoronix reader pointed out this approach to handling systemd-networkd and forcing it on by default (rather than making it an option to be enabled) was discouraging. Additionally, with it being enabled by default, systemd-networkd will be a daemon that still runs even if it was not configured. The systemd-networkd will just run and remain a running daemon without doing anything until it's configured.
In going through the latest Git code, there was a change to not statically enable systemd-networkd but then the next commit to systemd just minutes later enabled networkd by default. At least with the latest work, it's possible to run systemd disable systemd-networkd to disable this service if you don't wish to have systemd managing network functionality, but it will still be on by default.
This networkd component has been frustrating some early adopters of systemd 209 so we'll see if any further changes are made in time for systemd 210.