Merge branch 'Rate-adaptation-for-Felix-DSA-switch'

Vladimir Oltean says:

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Rate adaptation for Felix DSA switch

When operating the MAC at 2.5Gbps (2500Base-X and USXGMII/QSXGMII) and
in combination with certain PHYs, it is possible that the copper side
may operate at lower link speeds. In this case, it is the PHY who has a
MAC inside of it that emits pause frames towards the switch's MAC,
telling it to slow down so that the transmission is lossless.

These patches are the support needed for the switch side of things to
work.
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Signed-off-by: David S. Miller <davem@davemloft.net>