net: lan966x: flower: add extack to lan966x_tc_flower_handler_control_usage()

Define extack locally, to reduce line lengths and aid future users.

Only compile-tested.
Signed-off-by: Asbjørn Sloth Tønnesen <ast@fiberby.net>
Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Reviewed-by: Horatiu Vultur <horatiu.vultur@microchip.com>
Link: https://lore.kernel.org/r/20240424125347.461995-2-ast@fiberby.netSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/microchip/lan966x/lan966x_tc_flower.c

@@ -45,6 +45,7 @@ static bool lan966x_tc_is_known_etype(struct vcap_tc_flower_parse_usage *st,
 static int
 lan966x_tc_flower_handler_control_usage(struct vcap_tc_flower_parse_usage *st)
 {
+	struct netlink_ext_ack *extack = st->fco->common.extack;
 	struct flow_match_control match;
 	int err = 0;
 
@@ -80,7 +81,7 @@ lan966x_tc_flower_handler_control_usage(struct vcap_tc_flower_parse_usage *st)
 	return err;
 
 out:
-	NL_SET_ERR_MSG_MOD(st->fco->common.extack, "ip_frag parse error");
+	NL_SET_ERR_MSG_MOD(extack, "ip_frag parse error");
 	return err;
 }