The MAC address of a network adapter being customized. The client cannot change
this value because the guest operating system has no control over the MAC
address of a virtual network adapter.
This property is optional. If it is not included, the customization process maps
the settings from the list of AdapterMappings.IPSettings in the
Specification.nicSettingMap to the virtual machine's network adapters, in PCI
slot order. The first virtual network adapter on the PCI bus is assigned
nicSettingMap.IPSettings, the second adapter is assigned
nicSettingMap.IPSettings, and so on.