r8169: align fix_features callback with vendor driver

This patch aligns the fix_features callback with the vendor driver and
also disables IPv6 HW checksumming and TSO if jumbo packets are used
on RTL8101/RTL8168/RTL8125.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>