net: dsa: Error out on tagging protocol mismatches

If there is a mismatch between enabled tagging protocols and the
protocol the switch supports, error out, rather than continue with a
situation which is unlikely to work.
Signed-off-by: Andrew Lunn <andrew@lunn.ch>
cc: alexander.h.duyck@intel.com
Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/dsa/dsa.c

@@ -174,8 +174,11 @@ dsa_switch_setup(struct dsa_switch_tree *dst, int index,
 			dst->rcv = brcm_netdev_ops.rcv;
 			break;
 #endif
-		default:
+		case DSA_TAG_PROTO_NONE:
 			break;
+		default:
+			ret = -ENOPROTOOPT;
+			goto out;
 		}
 
 		dst->tag_protocol = drv->tag_protocol;