dsa: mv88e6171: Fix tagging protocol/Kconfig

The mv88e6171 can support two different tagging protocols, DSA and
EDSA. The switch driver structure only allows one protocol to be
enumerated, and DSA was chosen. However the Kconfig entry ensures the
EDSA tagging code is built. With a minimal configuration, we then end
up with a mismatch. The probe is successful, EDSA tagging is used, but
the switch is configured for DSA, resulting in mangled packets.

Change the switch driver structure to enumerate EDSA, fixing the
mismatch.

Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Fixes: 42f27253

 ("net: DSA: Marvell mv88e6171 switch driver")
Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>