net: mscc: ocelot: delete PVID VLAN when readding it as non-PVID

net: mscc: ocelot: delete PVID VLAN when readding it as non-PVID

The following set of commands:

ip link add br0 type bridge vlan_filtering 1 # vlan_default_pvid 1 is implicit
ip link set swp0 master br0
bridge vlan add dev swp0 vid 1

should result in the dropping of untagged and 802.1p-tagged traffic, but
we see that it continues to be accepted. Whereas, had we deleted VID 1
instead, the aforementioned dropping would have worked

This is because the ANA_PORT_DROP_CFG update logic doesn't run, because
ocelot_vlan_add() only calls ocelot_port_set_pvid() if the new VLAN has
the BRIDGE_VLAN_INFO_PVID flag.

Similar to other drivers like mt7530_port_vlan_add() which handle this
case correctly, we need to test whether the VLAN we're changing used to
have the BRIDGE_VLAN_INFO_PVID flag, but lost it now. That amounts to a
PVID deletion and should be treated as such.

Regarding blame attribution: this never worked properly since the
introduction of bridge VLAN filtering in commit 7142529f1688 ("net:
mscc: ocelot: add VLAN filtering"). However, there was a significant
paradigm shift which aligned the ANA_PORT_DROP_CFG register with the
PVID concept rather than with the native VLAN concept, and that change
wasn't targeted for 'stable'. Realistically, that is as far as this fix
needs to be propagated to.

Fixes: be0576fed6d3 ("net: mscc: ocelot: move the logic to drop 802.1p traffic to the pvid deletion")
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Link: https://patch.msgid.link/20250424223734.3096202-1-vladimir.oltean@nxp.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>