Merge branch 'tcp_v6_gso_csum_prep'

Heiner Kallweit says:

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net: core: add helper tcp_v6_gso_csum_prep

Several network drivers for chips that support TSO6 share the same code
for preparing the TCP header, so let's factor it out to a helper.
A difference is that some drivers reset the payload_len whilst others
don't do this. This value is overwritten by TSO anyway, therefore
the new helper resets it in general.
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Signed-off-by: David S. Miller <davem@davemloft.net>