staging: most: net: use dormant state

This replaces the call of wait_for_completion in case of an invalid MAC
address in the function most_nd_open() with the dormant state of the
network device.

As a side effect, opening the network device cannot fail anymore.

Signed-off-by: Andrey Shvetsov <andrey.shvetsov@k2l.de>
Signed-off-by: Christian Gromm <christian.gromm@microchip.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>