qeth: enable scatter/gather by default

Set scatter/gather ON by default on OSA, for both layer 2 and
layer 3 modes. We always use fragmentation over QDIO anyway,
so let the upper layers of the stack take advantage of that.

Signed-off-by: Eugene Crosser <Eugene.Crosser@ru.ibm.com>
Signed-off-by: Ursula Braun <ubraun@linux.vnet.ibm.com>
Reviewed-by: Lakhvich Dmitriy <ldmitriy@ru.ibm.com>
Reviewed-by: Thomas Richter <tmricht@de.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>