netback: correct netbk_tx_err to handle wrap around.

[ Upstream commit b9149729 ]
Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Acked-by: Jan Beulich <JBeulich@suse.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

drivers/net/xen-netback/netback.c

@@ -852,7 +852,7 @@ static void netbk_tx_err(struct xenvif *vif,
 
 	do {
 		make_tx_response(vif, txp, XEN_NETIF_RSP_ERROR);
-		if (cons >= end)
+		if (cons == end)
 			break;
 		txp = RING_GET_REQUEST(&vif->tx, cons++);
 	} while (1);