usbnet: clear OPEN flag in failure path

Without clearing OPEN flag in failure path, runtime or system resume
may submit interrupt/rx URB and start tx queue mistakenly on a
interface in DOWN state.

Signed-off-by: Ming Lei <ming.lei@canonical.com>
Acked-by: Oliver Neukum <oneukum@suse.de>
Signed-off-by: David S. Miller <davem@davemloft.net>