Merge branch 'geneve-vxlan-mtu'

Stefano Brivio says:

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geneve, vxlan: Don't set exceptions if skb->len < mtu

This series fixes the exception abuse described in 2/2, and 1/2
is just a preparatory change to make 2/2 less ugly.
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Signed-off-by: David S. Miller <davem@davemloft.net>