de2104x: disable autonegotiation on broken hardware

At least on older 21041-AA chips (mine is rev. 11), TP duplex autonegotiation
causes the card not to work at all (link is up but no packets are transmitted).

de4x5 disables autonegotiation completely. But it seems to work on newer
(21041-PA rev. 21) so disable it only on rev<20 chips.

Signed-off-by: Ondrej Zary <linux@rainbow-software.org>
Acked-by: Jeff Garzik <jgarzik@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>