network: Keep a ref on NetDeviceEthernet while a edition dialog is open
Otherwise, invoking other panel (eg. through shell search, or CLI) and closing the dialog will result in a crash, as the NetDeviceEthernet object does no longer exist.
Otherwise, invoking other panel (eg. through shell search, or CLI) and closing the dialog will result in a crash, as the NetDeviceEthernet object does no longer exist.