sis900: generate fake MAC address if the hardware doesn't have one

The attached patch modifies the sis900 driver when the MAC address
read from the hardware is invalid. As suggested, the patch now
generates a random address so that the user can go on and use
the hardware. In any case a message is also shown to warn on the
unexpected condition.
This seems to happen with newer HW implementation of the sis900
chipset, since this never came up before.

Patch is against vanilla 2.6.28 (but the driver doesn't change so often,
so it will probably apply to older/newer versions too).

See bugzilla ID 10201 and 11649 and ignore the previous patch.

Signed-off-by: Daniele Venzano <venza@brownhat.org>
Signed-off-by: David S. Miller <davem@davemloft.net>