[PATCH] tulip DC21143 rev 48 10Mbit HDX fix

The patch below is necessary to allow my Digital DS21143 Tulip rev 48
ethernet interface to work in a 10Mbit Half Duplex network.  Without
it, the driver keeps retrying other modes in an endless loop.  It seems
like someone already had the same problem with a rev 65 board :)

Signed-off-by: Philippe De Muyter <phdm@macqel.be>
Signed-off-by: Jeff Garzik <jgarzik@pobox.com>