bpf, devmap: Move drop error path to devmap for XDP_REDIRECT

We want to change the current ndo_xdp_xmit drop semantics because it will
allow us to implement better queue overflow handling. This is working
towards the larger goal of a XDP TX queue-hook. Move XDP_REDIRECT error
path handling from each XDP ethernet driver to devmap code. According to
the new APIs, the driver running the ndo_xdp_xmit pointer, will break tx
loop whenever the hw reports a tx error and it will just return to devmap
caller the number of successfully transmitted frames. It will be devmap
responsibility to free dropped frames.

Move each XDP ndo_xdp_xmit capable driver to the new APIs:

- veth
- virtio-net
- mvneta
- mvpp2
- socionext
- amazon ena
- bnxt
- freescale (dpaa2, dpaa)
- xen-frontend
- qede
- ice
- igb
- ixgbe
- i40e
- mlx5
- ti (cpsw, cpsw-new)
- tun
- sfc

Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: Ioana Ciornei <ioana.ciornei@nxp.com>
Reviewed-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Reviewed-by: Camelia Groza <camelia.groza@nxp.com>
Acked-by: Edward Cree <ecree.xilinx@gmail.com>
Acked-by: Jesper Dangaard Brouer <brouer@redhat.com>
Acked-by: Shay Agroskin <shayagr@amazon.com>
Link: https://lore.kernel.org/bpf/ed670de24f951cfd77590decf0229a0ad7fd12f6.1615201152.git.lorenzo@kernel.org

drivers/net/xen-netfront.c

@@ -608,8 +608,8 @@ static int xennet_xdp_xmit(struct net_device *dev, int n,
 	struct netfront_info *np = netdev_priv(dev);
 	struct netfront_queue *queue = NULL;
 	unsigned long irq_flags;
-	int drops = 0;
-	int i, err;
+	int nxmit = 0;
+	int i;
 
 	if (unlikely(flags & ~XDP_XMIT_FLAGS_MASK))
 		return -EINVAL;
@@ -622,15 +622,13 @@ static int xennet_xdp_xmit(struct net_device *dev, int n,
 
 		if (!xdpf)
 			continue;
-		err = xennet_xdp_xmit_one(dev, queue, xdpf);
-		if (err) {
-			xdp_return_frame_rx_napi(xdpf);
-			drops++;
-		}
+		if (xennet_xdp_xmit_one(dev, queue, xdpf))
+			break;
+		nxmit++;
 	}
 	spin_unlock_irqrestore(&queue->tx_lock, irq_flags);
 
-	return n - drops;
+	return nxmit;
 }
 
 
@@ -875,7 +873,9 @@ static u32 xennet_run_xdp(struct netfront_queue *queue, struct page *pdata,
 		get_page(pdata);
 		xdpf = xdp_convert_buff_to_frame(xdp);
 		err = xennet_xdp_xmit(queue->info->netdev, 1, &xdpf, 0);
-		if (unlikely(err < 0))
+		if (unlikely(!err))
+			xdp_return_frame_rx_napi(xdpf);
+		else if (unlikely(err < 0))
 			trace_xdp_exception(queue->info->netdev, prog, act);
 		break;
 	case XDP_REDIRECT: