via-velocity: Turn scatter-gather support back off.

It causes all kinds of DMA API debugging assertions and
all straight-forward attempts to fix it have failed.

So turn off SG, and we'll tackle making this work
properly in net-next-2.6

Reported-by: Dave Jones <davej@redhat.com>
Tested-by: Dave Jones <davej@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>