I tried your solution ...You can see in the snap shot that userc cannot start and stop the device.
But yet they are given the option to disconnect on the top network icon.
I would like that users should not be able to disconnect or re-connect. The moment the Lan cable is connected to the router the network icon should indicate that network is ready. If the router is switche off the NW icon should shouw discconeted.
The user (other than root) should not be able to do anything.
Please see sketch. Help/suggestions would be very much appreciated.