staging: most: allocate private net_dev_context with the alloc_netdev

This moves the allocation of the net_dev to the aim_probe_channel() and
uses the parameter sizeof_priv of the function alloc_netdev to reserve
the space for the struct net_dev_context.

As a side effect, the nd->dev always points to the existing net_dev.

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>