networkmanager service: support changing the mac-address (#23464)

Set `networking.networkmanager.wifi.macAddress` or `networking.networkmanager.ethernet.macAddress`
to one of these values to change your macAddress.

* "XX:XX:XX:XX:XX:XX": set the MAC address of the interface.
* "permanent": use the permanent MAC address of the device.
* "preserve": don’t change the MAC address of the device upon activation.
* "random": generate a randomized value upon each connect.
* "stable": generate a stable, hashed MAC address.

See https://blogs.gnome.org/thaller/2016/08/26/mac-address-spoofing-in-networkmanager-1-4-0/ for more information