[PATCH] sky2: disable rx checksum on Yukon XL

Under load, my SysKonnect SK-9S22 sees duplicate checksums from
earlier packets.  Doesn't happen on other platforms so just disable
receive checksum there.

Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: Jeff Garzik <jgarzik@pobox.com>