Merge branch 'mv88e6xxx-mtu-fixes'

Andrew Lunn says:

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mv88e6xxx: MTU fixes

These three patches fix MTU issues reported by 曹煜.

There are two different ways of configuring the MTU in the hardware.
The 6161 family is using the wrong method. Some of the marvell switch
enforce the MTU when the port is used for CPU/DSA, some don't.
Because of the extra header, the MTU needs increasing with this
overhead.
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Signed-off-by: David S. Miller <davem@davemloft.net>