net: mscc: ocelot: allow unregistered IP multicast flooding

Flooding of unregistered IP multicast has been broken (both to other
switch ports and to the CPU) since the ocelot driver introduction, and
up until commit 4cf35a2b ("net: mscc: ocelot: fix broken IP
multicast flooding"), a bug fix for commit 421741ea ("net: mscc:
ocelot: offload bridge port flags to device") from v5.12.

The driver used to set PGID_MCIPV4 and PGID_MCIPV6 to the empty port
mask (0), which made unregistered IPv4/IPv6 multicast go nowhere, and
without ever modifying that port mask at runtime.

The expectation is that such packets are treated as broadcast, and
flooded according to the forwarding domain (to the CPU if the port is
standalone, or to the CPU and other bridged ports, if under a bridge).

Since the aforementioned commit, the limitation has been lifted by
responding to SWITCHDEV_ATTR_ID_PORT_BRIDGE_FLAGS events emitted by the
bridge. As for host flooding, DSA synthesizes another call to
ocelot_port_bridge_flags() on the NPI port which ensures that the CPU
gets the unregistered multicast traffic it might need, for example for
smcroute to work between standalone ports.

But between v4.18 and v5.12, IP multicast flooding has remained unfixed.

Delete the inexplicable premature optimization of clearing PGID_MCIPV4
and PGID_MCIPV6 as part of the init sequence, and allow unregistered IP
multicast to be flooded freely according to the forwarding domain
established by PGID_SRC, by explicitly programming PGID_MCIPV4 and
PGID_MCIPV6 towards all physical ports plus the CPU port module.

Fixes: a556c76a

 ("net: mscc: Add initial Ocelot switch support")
Cc: stable@kernel.org
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>