docs: fix info about representor identification

Update the "How are representors identified?" documentation
subchapter. For newer kernels driver should use
SET_NETDEV_DEVLINK_PORT instead of ndo_get_devlink_port()
callback.

Fixes: 7712b3e966ea ("Merge branch 'net-fix-netdev-to-devlink_port-linkage-and-expose-to-user'")
Signed-off-by: Mateusz Polchlopek <[e-mail]>
Reviewed-by: Wojciech Drewek <[e-mail]>
Reviewed-by: Przemek Kitszel <[e-mail]>
Reviewed-by: Edward Cree <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

Documentation/networking/representors.rst

···
 The representor netdevice should *not* directly refer to a PCIe device (e.g.
 through ``net_dev->dev.parent`` / ``SET_NETDEV_DEV()``), either of the
 representee or of the switchdev function.
-Instead, it should implement the ``ndo_get_devlink_port()`` netdevice op, which
-the kernel uses to provide the ``phys_switch_id`` and ``phys_port_name`` sysfs
-nodes.  (Some legacy drivers implement ``ndo_get_port_parent_id()`` and
+Instead, the driver should use the ``SET_NETDEV_DEVLINK_PORT`` macro to
+assign a devlink port instance to the netdevice before registering the
+netdevice; the kernel uses the devlink port to provide the ``phys_switch_id``
+and ``phys_port_name`` sysfs nodes.
+(Some legacy drivers implement ``ndo_get_port_parent_id()`` and
 ``ndo_get_phys_port_name()`` directly, but this is deprecated.)  See
 :ref:`Documentation/networking/devlink/devlink-port.rst <devlink_port>` for the
 details of this API.