NTB: Do not advance transport RX on link down

On link down, don't advance RX index to the next entry.  The next entry
should never be valid after receiving the link down flag.
Signed-off-by: NAllen Hubbe <Allen.Hubbe@emc.com>
Signed-off-by: NJon Mason <jdmason@kudzu.us>

drivers/ntb/ntb_transport.c

@@ -1212,8 +1212,7 @@ static int ntb_process_rxc(struct ntb_transport_qp *qp)
 		dev_dbg(&qp->ndev->pdev->dev, "link down flag set\n");
 		ntb_qp_link_down(qp);
 		hdr->flags = 0;
-		iowrite32(qp->rx_index, &qp->rx_info->entry);
-		return 0;
+		return -EAGAIN;
 	}
 
 	if (hdr->ver != (u32)qp->rx_pkts) {