Comment 32 for bug 1671951

See comment #20; ipv6 mtu is 1280 -> DEVICE_MTU.

I'm testing something in the middle now.

On Eoan with:

network:
    version: 2
    ethernets:
        ens3:
            addresses: [10.5.0.16/16]
            gateway4: 10.5.0.1
            dhcp4: false
            match:
                macaddress: fa:16:3e:c9:1e:fb
            mtu: 8958
            ipv6-mtu: 8960
            set-name: ens3
            nameservers:
                addresses: [10.5.0.2]
                search: [project.serverstack]

It works. Now on bionic-proposed, it does not.

Aug 28 16:59:56.659125 b-test-ipv6-mtu systemd-networkd[1149]: /run/systemd/network/10-netplan-ens3.network:11: Unknown lvalue 'IPv6MTUBytes' in section 'Network'

So, looks like bionic systemd is missing something.