[NET]: Add ethtool support for NETIF_F_IPV6_CSUM devices.

Add ethtool utility function to set or clear IPV6_CSUM feature flag.
Modify tg3.c and bnx2.c to use this function when doing ethtool -K
to change tx checksum.

Signed-off-by: Michael Chan <mchan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/linux/ethtool.h b/include/linux/ethtool.h
index f2d248f..3a63224 100644
--- a/include/linux/ethtool.h
+++ b/include/linux/ethtool.h
@@ -265,6 +265,7 @@
 u32 ethtool_op_get_tx_csum(struct net_device *dev);
 int ethtool_op_set_tx_csum(struct net_device *dev, u32 data);
 int ethtool_op_set_tx_hw_csum(struct net_device *dev, u32 data);
+int ethtool_op_set_tx_ipv6_csum(struct net_device *dev, u32 data);
 u32 ethtool_op_get_sg(struct net_device *dev);
 int ethtool_op_set_sg(struct net_device *dev, u32 data);
 u32 ethtool_op_get_tso(struct net_device *dev);