To access the netdevice of the GID attribute, use an existing API
rdma_read_gid_attr_ndev_rcu().

This further reduces dependency on open access to netdevice of GID
attribute.
Signed-off-by: NParav Pandit <parav@mellanox.com>
Signed-off-by: NLeon Romanovsky <leonro@mellanox.com>
Signed-off-by: NJason Gunthorpe <jgg@mellanox.com>