[IPV6]: Segmentation offload not set correctly on TCP children

TCP over IPV6 would incorrectly inherit the GSO settings.
This would cause kernel to send Tcp Segmentation Offload packets for
IPV6 data to devices that can't handle it. It caused the sky2 driver
to lock http://bugzilla.kernel.org/show_bug.cgi?id=7050
and the e1000 would generate bogus packets. I can't blame the
hardware for gagging if the upper layers feed it garbage.

This was a new bug in 2.6.18 introduced with GSO support.

Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: David S. Miller <davem@davemloft.net>