A user can change the operational GUID (a.k.a affective GUID) through
link/infiniband. Therefore it is preferred to return the currently set
GUID if it exists instead of the operational.

This way the PF can query which VF GUID will be set in the next bind.  In
order to align with MAC address, zero is returned if administrative GUID
is not set.

For example, before setting administrative GUID:
 $ ip link show
 ib0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 4092 qdisc mq state UP mode DEFAULT group default qlen 256
 link/infiniband 00:00:00:08:fe:80:00:00:00:00:00:00:52:54:00:c0:fe:12:34:55 brd 00:ff:ff:ff:ff:12:40:1b:ff:ff:00:00:00:00:00:00:ff:ff:ff:ff
 vf 0     link/infiniband 00:00:00:08:fe:80:00:00:00:00:00:00:52:54:00:c0:fe:12:34:55 brd 00:ff:ff:ff:ff:12:40:1b:ff:ff:00:00:00:00:00:00:ff:ff:ff:ff,
 spoof checking off, NODE_GUID 00:00:00:00:00:00:00:00, PORT_GUID 00:00:00:00:00:00:00:00, link-state auto, trust off, query_rss off

Then:

 $ ip link set ib0 vf 0 node_guid 11:00:af:21:cb:05:11:00
 $ ip link set ib0 vf 0 port_guid 22:11:af:21:cb:05:11:00

After setting administrative GUID:
 $ ip link show
 ib0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 4092 qdisc mq state UP mode DEFAULT group default qlen 256
 link/infiniband 00:00:00:08:fe:80:00:00:00:00:00:00:52:54:00:c0:fe:12:34:55 brd 00:ff:ff:ff:ff:12:40:1b:ff:ff:00:00:00:00:00:00:ff:ff:ff:ff
 vf 0     link/infiniband 00:00:00:08:fe:80:00:00:00:00:00:00:52:54:00:c0:fe:12:34:55 brd 00:ff:ff:ff:ff:12:40:1b:ff:ff:00:00:00:00:00:00:ff:ff:ff:ff,
 spoof checking off, NODE_GUID 11:00:af:21:cb:05:11:00, PORT_GUID 22:11:af:21:cb:05:11:00, link-state auto, trust off, query_rss off

Fixes: 9c0015ef ("IB/mlx5: Implement callbacks for getting VFs GUID attributes")
Link: https://lore.kernel.org/r/20200116120048.12744-1-leon@kernel.orgSigned-off-by: Danit Goldberg <danitg@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>