Where #743 adds a bridge network to a running container, this adds mapped vSphere networks that require PCI hotadd of a new vNIC. The workflow in the portlayer should be identical to the pseudo-code in #743. The network.Join operation adding a DeviceChange entry for the new NIC should be invisible to the callers.

On the tether side this requires hotadd and configuration of the new vNIC. This may not require #742 as the hotadd event itself can be used as a trigger, as such I do not consider it a dependency for this work.