Enable DHCPv6 client
Set DHCP=yes
in /etc/systemd/network/80-dhcp.network
to start both
DHCPv4 and DHCPv6 clients. This provides IPv6 for networks using DHCPv6
without RA.
It should not have much effect of networks with working RA since the
IPv6AcceptRA
option is enabled by default for these connections anyway.