Support for configuring more netplan options

[chancez]

Description

I specifically would like a way to set the use-routes and use-domains option on a given interface in the network-configuration userdata used by netplan so I can disable the default route created for the socket_vmnet interface, as it causes problems when my VPN is active, as internet bound connections fail unless they go over the usermode network. Additionally, I need to set the use-domains option for similar reasons.

Eg:

ethernets:
  lima1:
    dhcp4-overrides:
      use-routes: false
      use-domains: false

I've got a partial work-around by increasing the metric of the 'shared' network in my lima.yaml, but the default route still exists, so it can still be used, which still causes problems. However, my next issue is DNS. systemd-resolved is sending DNS queries over both interfaces, and this leads to issues with my VPN. It has to wait for a timeout on the queries going over the socket_vmnet interface because the packets just get blackholed (or something) due to the VPN.

Currently I'm trying to hack around this in provision scripts calling ip route del default dev lima1, but I'm having trouble figuring out how to do the equivalent of use-domains without directly setting UseDomains=false in the /run/systemd/network/10-netplan-lima1.network or use-domains: false in the /etc/netplan/50-cloud-init.yaml and re-running netplan apply.

So ideally I could just set some netplan options directly which would simplify all of this.

[chancez]

Here's my current work around to deal with VPN issues:

- mode: system
  script: |
    #!/bin/bash
    set -eux -o pipefail

    # Disable fqdn option in sudoers, it's not necessary
    echo 'Defaults !fqdn' > /etc/sudoers.d/no-fqdn

    # Disable the default route and search domains for the socket_vmnet
    # interface as it causes issues when on VPN, as we want all queries and
    # network requests to the internet to use the usermode network
    mkdir -p /run/systemd/network/10-netplan-lima1.network.d/
    cat <<EOF > /run/systemd/network/10-netplan-lima1.network.d/disable-options.conf
    [DHCP]
    UseRoutes=false
    UseDomains=false
    EOF
    systemctl restart systemd-networkd
    # Sleep before moving on to avoid issues resolving in the next step
    sleep 5