net: dsa: propagate extack to port_lag_join

Drivers could refuse to offload a LAG configuration for a variety of
reasons, mainly having to do with its TX type. Additionally, since DSA
masters may now also be LAG interfaces, and this will translate into a
call to port_lag_join on the CPU ports, there may be extra restrictions
there. Propagate the netlink extack to this DSA method in order for
drivers to give a meaningful error message back to the user.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
diff --git a/net/dsa/dsa_priv.h b/net/dsa/dsa_priv.h
index d252a04..f0ae54d 100644
--- a/net/dsa/dsa_priv.h
+++ b/net/dsa/dsa_priv.h
@@ -88,6 +88,7 @@ struct dsa_notifier_lag_info {
 	const struct dsa_port *dp;
 	struct dsa_lag lag;
 	struct netdev_lag_upper_info *info;
+	struct netlink_ext_ack *extack;
 };
 
 /* DSA_NOTIFIER_VLAN_* */