net: ethernet: mtk_eth_soc: flower: validate control flags

This driver currently doesn't support any control flags.

Use flow_rule_has_control_flags() to check for control flags,
such as can be set through `tc flower ... ip_flags frag`.

In case any control flags are masked, flow_rule_has_control_flags()
sets a NL extended error message, and we return -EOPNOTSUPP.

Only compile-tested.
Signed-off-by: Asbjørn Sloth Tønnesen <ast@fiberby.net>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://lore.kernel.org/r/20240418161821.189263-1-ast@fiberby.netSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/mediatek/mtk_ppe_offload.c

@@ -273,6 +273,10 @@ mtk_flow_offload_replace(struct mtk_eth *eth, struct flow_cls_offload *f,
 
 		flow_rule_match_control(rule, &match);
 		addr_type = match.key->addr_type;
+
+		if (flow_rule_has_control_flags(match.mask->flags,
+						f->common.extack))
+			return -EOPNOTSUPP;
 	} else {
 		return -EOPNOTSUPP;
 	}