Support RFC 8925 (IPv6-Only Preferred Option for DHCPv4) dhcp option 108 AKA IPv6-Mostly

Add support for (https://www.rfc-editor.org/rfc/rfc8925.html) IPv6-mostly AKA dhcp option 108. This is primarily a client side option so it would be implemented in the NM dhcp client.

It allows the use/prioritization of IPv6 on a network that supports dual stack v4/v6. It allows the use of pure IPv6 in a dual stack v4/v6 network. Option 108 is already supported on Android/iOS/MacOS.

More details in this RIPE presentation: https://www.ipv6.org.uk/wp-content/uploads/2023/02/08_UKIPv6-Deploying_IPv6_mostly.pdf

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