When RX/TX checksum offloading is turned on and the adapter is
an OSA 3 card in layer 3 mode, the checksum offloading is only
performed when both peers use different adapters. If both peers
share an OSA 3 card, communication is a memory copy and
checksum offloading is not performed.

This patch adds a warning to inform the administrator.

OSA 3 in layer 2 mode does not offer the RX/TX checksum
offload feature.
Signed-off-by: NThomas Richter <tmricht@linux.vnet.ibm.com>
Reviewed-by: NJulian Wiedmann <jwi@linux.vnet.ibm.com>
Reviewed-by: NUrsula Braun <ubraun@linux.vnet.ibm.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>