Use the sgid and other information from the path record to figure out the
sgid_attrs.

Store the selected table entry in the sgid_attr for everything else to
use.
Signed-off-by: NParav Pandit <parav@mellanox.com>
Signed-off-by: NJason Gunthorpe <jgg@mellanox.com>
Signed-off-by: NLeon Romanovsky <leonro@mellanox.com>