be2net: Bug fix to properly update ethtool tx-checksumming after ethtool -K <ifname> tx off

This is a fix for a bug which was a result of wrong use of checksum offload flag.
The status of tx-checksumming was not changed from on to off
after a 'ethtool -K <ifname> tx off' operation.
Use the proper checksum offload flag NETIF_F_HW_CSUM instead of
NETIF_F_IP_CSUM and NETIF_F_IPV6_CSUM.
Patch is against net-2.6 tree.

Signed-off-by: Ajit Khaparde <ajitk@serverengines.com>
Signed-off-by: David S. Miller <davem@davemloft.net>