staging: slicoss: notifiy network stack about change in link state

Notify the network stack about link states via netif_carrier_[off|on]().
Also set the link state off initially and when the interface is brought
down.

Signed-off-by: Lino Sanfilippo <LinoSanfilippo@gmx.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>