IB/core: Specify attribute_id in port_table_attribute

Add the attr_id on port_table_attribute since we will have to add
a different port_table_attribute for the extended attribute soon.

Reviewed-by: Hal Rosenstock <hal@mellanox.com>
Signed-off-by: Christoph Lameter <cl@linux.com>
Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>