IB/mlx4: Manage admin alias GUID upon admin request

Set the admin alias GUID per the administrator's request via the sysfs
mechanism into the core layer.

The "get" request returns the current value. However, if the administrator
requests the SM to assign a new value by requesting 0, the SM assigned
GUID is returned.

Signed-off-by: Yishai Hadas <yishaih@mellanox.com>
Signed-off-by: Jack Morgenstein <jackm@dev.mellanox.co.il>
Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>