It's confusing that GetMachineNetworksFromBootstrapHost() returns the
existing MachineNetworks in the cluster (and does *not* get them from
the bootstrap host) if they already exist there. Refactor to make the
logic clearer.

The network type is set for all platforms in getBasicInstallConfig().
There is no need to set it again in the none platform provider.

None of the subnets specified in any of the machineNetworks,
clusterNetworks, or serviceNetworks should overlap. Validate all of
these combinations, as openshift-installer does, instead of making
assumptions about indices being aligned to address families.

Don't make assumptions about a 1:1 mapping between MachineNetworks and
VIPs.

In the belongs-to-machine-cidr validation, allow the host to be a member
of any MachineNetwork. In a dual-stack cluster, require it to be a
member of both an IPv4 and an IPv6 network.

Previously it was assumed that the only reason for multiple
MachineNetworks to appear was that a dual stack cluster could contain
exactly one IPv4 and one IPv6 MachineNetwork.

Multiple MachineNetworks in the same address family and IPv6-primary
dual-stack clusters are a thing, so relax the dual-stack validation
requirements for machine networks to allow them.

Allow users to specify multiple machine networks of the same address
family. This is a documented and supported feature of OpenShift.

This reverts commit 873dd81.

Don't restrict ourselves to the first machine networking when looking
for an interface on a machine network to set the BootMACAddress.

OpenShift has ~always supported having machines in multiple
machineNetworks, so update the TODO comment to reflect that accounting
for this is already something we need to do to fully support
non-UserManagedNetworking clusters. (UserManagedNetworking clusters use
only the L3 connectivity check.)

See https://issues.redhat.com/browse/OCPBUGS-30730 for more details.