mlxsw: spectrum: Improve IPv6 unregistered multicast flooding

Up until now IPv6 unregistered multicast traffic would be flooded like
broadcast, even when MLD snooping was enabled on the bridge. This was
intentional as MLD packet traps were missing, preventing the bridge
driver from programming MDB entries to the device.

Previous patch added these traps, so we can now finally flood IPv6
unregistered multicast packets to specific ports via the multicast table
instead of flooding them to all ports via the broadcast table.

Signed-off-by: Arkadi Sharshevsky <arkadis@mellanox.com>
Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>