staging: slicoss: start tx queue when interface is brought up

There is no reason to delay tx queue activation until a link is detected.
So start the queue when the interface is brought up and stop it when the
interface is brought down.

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