networkd: do not use DHCP for bridge devices

[pothos]

The main change:

• networkd: do not use DHCP for special devices

We are always lagging behind with which interface names are used by
CNIs and have to be set Unmanaged so that we don't use DHCP for them.

Go the other way round and exclude special devices which won't use DHCP
upfront so that we don't even try configuring them this way. Bridges
normally don't get their IP address assinged via DHCP and if someone
wants that, they are free to ship their own networkd unit. Same for
tunnel devices and similar. If this causes problems, we can revert this
because we still have the explicit rules but eventually this should
allow us to retire some of our rules that match by interface name.

A drive-by fix which is still relevant in case we have revert the main change:

• networkd: prevent networkd interference with calico vxlan interface

The Calico vxlan interface was getting the default networkd
configuration applied which tries to attach an IP address through DHCP.
This meant that the interface was stuck in this "configuring" state by
networkd and this is also a potential source of disruption as reported
in similar cases.

Set the vxlan.calico interface to be excluded from networkd (unmanaged)
because it is set up manually by Calico and not through DHCP.

How to use

Testing done

[krnowak]

Would this change mean that #55 is not necessary and other network files excluding specific bridge devices could also be dropped?

[pothos]

Would this change mean that #55 is not necessary and other network files excluding specific bridge devices could also be dropped?

Maybe yes but this is also something that could be reverted if it makes problems, I would keep the specific rules we have for the mean time.

[krnowak]

Looks good. I suppose it will be release-notes-worthy change.

[pothos]

Looks good. I suppose it will be release-notes-worthy change.

Right, added it in the coreos-overlay PR and can make it even more verbose if wanted