At the very least we should probably move the skb->offload_fwd_mark
setting down into the individual taggers since they should be in a
better position to set it or not based on the switch device they are
driving, this should address, on a per-switch basis whether 2) or 3)
applies to a given switch.

Yes, that could be done.

That being said, I have a feeling that the Marvell switches behave a
tiny bit differently than others in that they do not flood broadcast by
default in a given L2 domain.

It seems like the switch can be configured to flood broadcast. Just at
the moment, it is not.

On b53/bcm_sf2 there is the ability to disable the reception of
broadcast frames on the management/CPU port, and while there is the
ability to configure which ports should be flooded in case of
unicast/multicast lookup failures, I don't see anything for Broadcast,
so I am assuming this will get forwarded by default. Will test with your
patch set later on time permitting.

Please let me know the results of the tests.

If Marvell is being different, it also means that all other switches
today are duplicating broadcasts. We should fix that. In fact, i think
we need to fix this first, before these patches for IGMP snooping on
br0 goes in.

    Andrew