[TG3]: Enable auto MDI.

This patch adds automatic MDI crossover support when autonegotiation is
turned off.  Automatic MDI crossover allows link to be established
without the use of a crossover cable.

Signed-off-by: Matt Carlson <mcarlson@broadcom.com>
Signed-off-by: Michael Chan <mchan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>