If the tg3 interface is down, the driver will return ethtool stats
uninitialized.  This patch zeroes out the destination stat buffer in
such a case.
Signed-off-by: NMatt Carlson <mcarlson@broadcom.com>
Reviewed-by: NMichael Chan <mchan@broadcom.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>