Merge branch 'net-stmmac-fix-handling-of-oversized-frames'

Aaro Koskinen says:

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net: stmmac: fix handling of oversized frames

I accidentally had MTU size mismatch (9000 vs. 1500) in my network,
and I noticed I could kill a system using stmmac & 1500 MTU simply
by pinging it with "ping -s 2000 ...".

While testing a fix I encountered also some other issues that need fixing.

I have tested these only with enhanced descriptors, so the normal
descriptor changes need a careful review.
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Signed-off-by: David S. Miller <davem@davemloft.net>