net: dsa: Refactor transmit path to eliminate duplication

All tagging protocols do the same thing: increment device statistics,
make room for the tag to be inserted, create the tag, invoke the parent
network device transmit function.

In order to prepare for adding netpoll support, which requires the tag
creation, but not using the parent network device transmit function, do
some little refactoring which eliminates duplication between the 4
tagging protocols supported.

We need to return a sk_buff pointer back to the caller because the tag
specific transmit function may have to reallocate the original skb (e.g:
tag_trailer.c) and this is the one we should be transmitting, not the
original sk_buff we were passed.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/dsa/tag_dsa.c b/net/dsa/tag_dsa.c
index 2dab2706..aa780e4 100644
--- a/net/dsa/tag_dsa.c
+++ b/net/dsa/tag_dsa.c
@@ -15,14 +15,11 @@
 
 #define DSA_HLEN	4
 
-static netdev_tx_t dsa_xmit(struct sk_buff *skb, struct net_device *dev)
+static struct sk_buff *dsa_xmit(struct sk_buff *skb, struct net_device *dev)
 {
 	struct dsa_slave_priv *p = netdev_priv(dev);
 	u8 *dsa_header;
 
-	dev->stats.tx_packets++;
-	dev->stats.tx_bytes += skb->len;
-
 	/*
 	 * Convert the outermost 802.1q tag to a DSA tag for tagged
 	 * packets, or insert a DSA tag between the addresses and
@@ -63,14 +60,11 @@
 		dsa_header[3] = 0x00;
 	}
 
-	skb->dev = p->parent->dst->master_netdev;
-	dev_queue_xmit(skb);
-
-	return NETDEV_TX_OK;
+	return skb;
 
 out_free:
 	kfree_skb(skb);
-	return NETDEV_TX_OK;
+	return NULL;
 }
 
 static int dsa_rcv(struct sk_buff *skb, struct net_device *dev,