Comment 1 for bug 1789521

I talked to Andres a little bit about this, and he had another good suggestion: if the pod host is a deployed machine in MAAS, we know where it PXE booted from. That could be a good indicator that the same bridge is valid to boot from, even in the absence of DHCP (or DHCP relay) enabled in MAAS.

Further, we could look at enhancing external DHCP detection as a way to test to see if PXE booting via MAAS is properly enabled for an external DHCP server.

I think these tasks can be handled separately from the primary fix for this issue, but one thing we could do in order to ensure backward compatibility in the case of external DHCP is to allow booting from the `maas` network in libvirt by default *if and only if libvirt's DHCP is not enabled*. This would allow the scenario where external DHCP could have been enabled already (and the fact that someone has a `maas` network in libvirt is a very specific thing to do, so it's likely to infer that as the user's intent.)