IB/mlx4: Request alias GUID on demand

Request GIDs from the SM on demand, i.e., when a VF actually needs them,
and release them when the GIDs are no longer in use.

In cloud environments, this is useful for GID migrations, in which a
GID is assigned to a VF on the destination HCA, while the VF on the
source HCA is shutdown (but the GID was not administratively released).

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>