rtnetlink: return the correct error code

Before this patch, function ndo_dflt_fdb_dump() will always return code
from uc fdb dump. The reture code of mc fdb dump is lost.
Signed-off-by: NZhang Shengju <zhangshengju@cmss.chinamobile.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/core/rtnetlink.c

@@ -3177,7 +3177,7 @@ int ndo_dflt_fdb_dump(struct sk_buff *skb,
 	err = nlmsg_populate_fdb(skb, cb, dev, idx, &dev->uc);
 	if (err)
 		goto out;
-	nlmsg_populate_fdb(skb, cb, dev, idx, &dev->mc);
+	err = nlmsg_populate_fdb(skb, cb, dev, idx, &dev->mc);
 out:
 	netif_addr_unlock_bh(dev);
 	return err;