link state with the new usb_net driver

[Pirmin Duss]

Hello Genodians

While testing my changed usb_net driver that supports SMSC95XX on 
arm_v8a I discovered, that the link state isn't propagated to the 
connected nic_router as it has been with the old version.

With the old driver the log output of nic_router was as follows when the 
cable was connected/disconnected:

<connect cable>
[init -> nic_router] [secondary_nic] NIC sessions: 1
[init -> nic_router] [secondary_nic] dynamic IP config: interface 
10.10.10.10/16, ...

<disconnect cable>
[init -> nic_router] [secondary_nic] dynamic IP config: none
[init -> nic_router] [secondary_nic] NIC sessions: 0


With the new driver nic_router always reports:

[init -> nic_router] [secondary_nic] NIC sessions: 1


As I do not have any other devices that need the usb_net driver,
I'm not sure, if this only happens for my driver or if this is 
consistent with all other device types.

Could someone with an other usb_net driven device give me feedback, if
other devices show the same log outputs?

Regards, Pirmin