Just about nothing actually uses networkd
"In addition to Ubuntu and Red Hat Enterprise Linux, Systemd has been adopted as a service manager for Debian, Fedora, CoreOS, Mint, and SUSE Linux Enterprise Server. We're told RHEL 7, at least, does not use the vulnerable component by default."
I can tell you for sure that no version of Fedora does, either, and I'm fairly sure that neither does Debian, SLES or Mint. I don't know anything much about CoreOS, but https://coreos.com/os/docs/latest/network-config-with-networkd.html suggests it actually *might* use systemd-networkd.
systemd-networkd is not part of the core systemd init daemon. It's an optional component, and most distros use some other network manager (like NetworkManager or wicd) by default.
Biting the hand that feeds IT
