net: dsa: Add support for querying supported bridge flags

The DSA drivers do not support bridge flags offload. Yet, this attribute
should be added in order for the bridge to fail when one tries set a
flag on the port, as explained in commit dc0ecab ("net: switchdev:
Add support for querying supported bridge flags by hardware").

Signed-off-by: Arkadi Sharshevsky <[email protected]>
Reviewed-by: Vivien Didelot <[email protected]>
Reviewed-by: Florian Fainelli <[email protected]>
Signed-off-by: David S. Miller <[email protected]>

Author: Arkadi Sharshevsky

net/dsa/slave.c

@@ -324,6 +324,9 @@ static int dsa_slave_port_attr_get(struct net_device *dev,
 		attr->u.ppid.id_len = sizeof(ds->index);
 		memcpy(&attr->u.ppid.id, &ds->index, attr->u.ppid.id_len);
 		break;
+	case SWITCHDEV_ATTR_ID_PORT_BRIDGE_FLAGS_SUPPORT:
+		attr->u.brport_flags_support = 0;
+		break;
 	default:
 		return -EOPNOTSUPP;
 	}