forcedeth: fix checksum flag

forcedeth: fix checksum flag

Fix the checksum feature advertised in device flags.  The hardware support
TCP/UDP over IPv4 and TCP/UDP over IPv6 (without IPv6 extension headers).
However, the kernel feature flags do not distinguish IPv6 with/without
extension headers.

Therefore, the driver needs to use NETIF_F_IP_CSUM instead of
NETIF_F_HW_CSUM since the latter includes all IPv6 packets.

A future patch can be created to check for extension headers and perform
software checksum calculation.

Signed-off-by: Ayaz Abdulla <[email protected]>
Cc: Jeff Garzik <[email protected]>
Cc: Manfred Spraul <[email protected]
Cc: <[email protected]>		[2.6.25.x, 2.6.26.x]
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Jeff Garzik <[email protected]>