I am using systemd to set the DHCP to use ipv4, but everyt ime the device (a Colibri VF50) starts up, I get an ipv6 address.
Maybe it would be good for you to familiarise yourself with some basic IPv6 networking concepts answering such trivia before posting any question.
Are you saying that you don’t get a IPv4 address? How does your configuration file exactly looks like? I am guessing you follow this article?