tg3: don't clear stats while tg3_close

Now tg3 NIC's stats will be cleared after ifdown/ifup. bond_get_stats traverse
its salves to get statistics,cumulative the increment.If a tg3 NIC is added to
bonding as a slave,ifdown/ifup will cause bonding's stats become tremendous value
(ex.1638.3 PiB) because of negative increment.

Fixes: 92feeabf3f67 ("tg3: Save stats across chip resets")
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/broadcom/tg3.c

@@ -11729,10 +11729,6 @@ static int tg3_close(struct net_device *dev)
 
 	tg3_stop(tp);
 
-	/* Clear stats across close / open calls */
-	memset(&tp->net_stats_prev, 0, sizeof(tp->net_stats_prev));
-	memset(&tp->estats_prev, 0, sizeof(tp->estats_prev));
-
 	if (pci_device_is_present(tp->pdev)) {
 		tg3_power_down_prepare(tp);