Code review comment for ~mgerdts/cloud-init:lp1765801

Upon further experimentation, I don't think that adding (per-datasource) apply_network_config is needed. Setting it can cause a previously working instance to no longer be reachable over the net.

Better is:

network: {config: disabled}

This allows a working config to persist in /etc/netplan/50-cloud-init.yaml while not making further changes on subsequent boots.