Merge branch 'dsa-cross-chip'

Vladimir Oltean says:

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Improvement for DSA cross-chip setups

This series improves some aspects in multi-switch DSA tree topologies:
- better device tree validation
- better handling of MTU changes
- better handling of multicast addresses
- removal of some unused code
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Signed-off-by: David S. Miller <davem@davemloft.net>