net-next: dsa: add Qualcomm tag RX/TX handler

Add support for the 2-bytes Qualcomm tag that gigabit switches such as
the QCA8337/N might insert when receiving packets, or that we need
to insert while targeting specific switch ports. The tag is inserted
directly behind the ethernet header.

Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: John Crispin <john@phrozen.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/dsa.h

@@ -26,6 +26,7 @@ enum dsa_tag_protocol {
 	DSA_TAG_PROTO_TRAILER,
 	DSA_TAG_PROTO_EDSA,
 	DSA_TAG_PROTO_BRCM,
+	DSA_TAG_PROTO_QCA,
 	DSA_TAG_LAST,		/* MUST BE LAST */
 };