net: dsa: change tag_protocol to an enum

Now that we introduced an additional multiplexing/demultiplexing layer
with commit 3e8a72d1dae37 ("net: dsa: reduce number of protocol hooks")
that lives within the DSA code, we no longer need to have a given switch
driver tag_protocol be an actual ethertype value, instead, we can
replace it with an enum: dsa_tag_protocol.

Do this replacement in the drivers, which allows us to get rid of the
cpu_to_be16()/htons() dance, and remove ETH_P_BRCMTAG since we do not
need it anymore.

Suggested-by: Alexander Duyck <alexander.duyck@gmail.com>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/dsa/mv88e6131.c b/drivers/net/dsa/mv88e6131.c
index 953bc6a..35541f2 100644
--- a/drivers/net/dsa/mv88e6131.c
+++ b/drivers/net/dsa/mv88e6131.c
@@ -379,7 +379,7 @@
 }
 
 struct dsa_switch_driver mv88e6131_switch_driver = {
-	.tag_protocol		= cpu_to_be16(ETH_P_DSA),
+	.tag_protocol		= DSA_TAG_PROTO_DSA,
 	.priv_size		= sizeof(struct mv88e6xxx_priv_state),
 	.probe			= mv88e6131_probe,
 	.setup			= mv88e6131_setup,