net: ethernet: ti: am65-cpsw: fix vlan offload for multi mac mode

The VLAN offload for AM65x CPSW2G is implemented using existing ALE APIs,
which are also used by legacy CPSW drivers.
So, now it always adds current Ext. Port and Host as VLAN members when VLAN
is added by 8021Q core (.ndo_vlan_rx_add_vid) and forcibly removes VLAN
from ALE table in .ndo_vlan_rx_kill_vid(). This works as for AM65x CPSW2G
(which has only one Ext. Port) as for legacy CPSW devices (which can't
support same VLAN on more then one Port in multi mac (dual-mac) mode). But
it doesn't work for the new J721E and AM64x multi port CPSWxG versions
doesn't have such restrictions and allow to offload the same VLAN on any
number of ports.

Now the attempt to add same VLAN on two (or more) K3 CPSWxG Ports will
cause:
 - VLAN members mask overwrite when VLAN is added
 - VLAN removal from ALE table when any Port removes VLAN

This patch fixes an issue by:
 - switching to use cpsw_ale_vlan_add_modify() instead of
   cpsw_ale_add_vlan() when VLAN is added to ALE table, so VLAN members
   mask will not be overwritten;
 - Updates cpsw_ale_del_vlan() as:
     if more than one ext. Port is in VLAN member mask
     then remove only current port from VLAN member mask
     else remove VLAN ALE entry

 Example:
  add: P1 | P0 (Host) -> members mask: P1 | P0
  add: P2 | P0        -> members mask: P2 | P1 | P0
  rem: P1 | P0        -> members mask: P2 | P0
  rem: P2 | P0        -> members mask: -

The VLAN is forcibly removed if port_mask=0 passed to cpsw_ale_del_vlan()
to preserve existing legacy CPSW drivers functionality.

Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
Reviewed-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>