devlink: Clarifies max_macs generic devlink param

The generic param max_macs documentation isn't clear.
Replace it with a more descriptive documentation

Signed-off-by: Shay Drory <shayd@nvidia.com>
Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>

Documentation/networking/devlink/devlink-params.rst

@@ -118,8 +118,10 @@ own name.
        errors.
    * - ``max_macs``
      - u32
-     - Specifies the maximum number of MAC addresses per ethernet port of
-       this device.
+     - Typically macvlan, vlan net devices mac are also programmed in their
+       parent netdevice's Function rx filter. This parameter limit the
+       maximum number of unicast mac address filters to receive traffic from
+       per ethernet port of this device.
    * - ``region_snapshot_enable``
      - Boolean
      - Enable capture of ``devlink-region`` snapshots.