nm-initrd-generator completely disables IPv4 for `ip=dhcp6`
ip=dhcp
generates a connection with both IPv4 and IPv6 enabled, but only IPv4 required.
ip=dhcp6
generates a connection with only IPv6 enabled (and required).
Instead, it should also enable IPv4 as optional.
Downstream: https://bugzilla.redhat.com/show_bug.cgi?id=1963971