dsa: add support for Trailer tagging format

This adds support for the Trailer switch tagging format.  This is
another tagging that doesn't explicitly mark tagged packets with a
distinct ethertype, so that we need to add a similar hack in the
receive path as for the Original DSA tagging format.

Signed-off-by: Lennert Buytenhek <buytenh@marvell.com>
Tested-by: Byron Bradley <byron.bbradley@gmail.com>
Tested-by: Tim Ellis <tim.ellis@mac.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/dsa/dsa_priv.h b/net/dsa/dsa_priv.h
index 2f1d68c..7063378 100644
--- a/net/dsa/dsa_priv.h
+++ b/net/dsa/dsa_priv.h
@@ -109,5 +109,8 @@
 /* tag_edsa.c */
 int edsa_xmit(struct sk_buff *skb, struct net_device *dev);
 
+/* tag_trailer.c */
+int trailer_xmit(struct sk_buff *skb, struct net_device *dev);
+
 
 #endif