net/mlx4_en: Fix bridged vSwitch configuration for non SRIOV mode

Commit 5b4c4d36 "mlx4_en: Allow communication between functions on
same host" introduced a regression under which a bridge acting as vSwitch
whose uplink is an mlx4 Ethernet device become non-operative in native
(non sriov) mode. This happens since broadcast ARP requests sent by VMs
were loopback-ed by the HW and hence the bridge learned VM source MACs
on both the VM and the uplink ports.

The fix is to place the DMAC in the send WQE only under SRIOV/eSwitch
configuration or when the device is in selftest.
Reviewed-by: NOr Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: NYan Burman <yanb@mellanox.com>
Signed-off-by: NAmir Vadai <amirv@mellanox.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/ethernet/mellanox/mlx4/en_tx.c

@@ -630,10 +630,15 @@ netdev_tx_t mlx4_en_xmit(struct sk_buff *skb, struct net_device *dev)
 		ring->tx_csum++;
 	}
 
-	/* Copy dst mac address to wqe */
+	if (mlx4_is_mfunc(mdev->dev) || priv->validate_loopback) {
+		/* Copy dst mac address to wqe. This allows loopback in eSwitch,
+		 * so that VFs and PF can communicate with each other
+		 */
 		ethh = (struct ethhdr *)skb->data;
 		tx_desc->ctrl.srcrb_flags16[0] = get_unaligned((__be16 *)ethh->h_dest);
 		tx_desc->ctrl.imm = get_unaligned((__be32 *)(ethh->h_dest + 2));
+	}
+
 	/* Handle LSO (TSO) packets */
 	if (lso_header_size) {
 		/* Mark opcode as LSO */