tg3: Relax EEE thresholds

The hardware defaults to fairly aggressive EEE thresholds.  While there
appear to be no ill effects, this patch relaxes them, just as a
precaution.

Signed-off-by: Matt Carlson <mcarlson@broadcom.com>
Reviewed-by: Benjamin Li <benli@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>