net: mscc: ocelot: add the local station MAC addresses in VID 0

The ocelot switchdev driver does not include the CPU port in the list of
flooding destinations for unknown traffic, instead that traffic is
supposed to match FDB entries to reach the CPU.

The addresses it installs are:
(a) the station MAC address, in ocelot_probe_port() and later during
    runtime in ocelot_port_set_mac_address(). These are the VLAN-unaware
    addresses. The VLAN-aware addresses are in ocelot_vlan_vid_add().
(b) multicast addresses added with dev_mc_add() (not bridge host MDB
    entries) in ocelot_mc_sync()
(c) multicast destination MAC addresses for MRP in ocelot_mrp_save_mac(),
    to make sure those are dropped (not forwarded) by the bridging
    service, just trapped to the CPU

So we can see that the logic is slightly buggy ever since the initial
commit a556c76a ("net: mscc: Add initial Ocelot switch support").
This is because, when ocelot_probe_port() runs, the port pvid is 0.
Then we join a VLAN-aware bridge, the pvid becomes 1, we call
ocelot_port_set_mac_address(), this learns the new MAC address in VID 1
(also fails to forget the old one, since it thinks it's in VID 1, but
that's not so important). Then when we leave the VLAN-aware bridge,
outside world is unable to ping our new MAC address because it isn't
learned in VID 0, the VLAN-unaware pvid.

[ note: this is strictly based on static analysis, I don't have hardware
  to test. But there are also many more corner cases ]

The basic idea is that we should have a separation of concerns, and the
FDB entries used for standalone operation should be managed by the
driver, and the FDB entries used by the bridging service should be
managed by the bridge. So the standalone and VLAN-unaware bridge FDB
entries should not follow the bridge PVID, because that will only be
active when the bridge is VLAN-aware. So since the port pvid is
coincidentally zero during probe time, just make those entries
statically go to VID 0.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>