flow_offload: improve extack msg for user when adding invalid filter

Add extack message to return exact message to user when adding invalid
filter with conflict flags for TC action.

In previous implement we just return EINVAL which is confusing for user.
Signed-off-by: Baowen Zheng <baowen.zheng@corigine.com>
Reviewed-by: Roi Dayan <roid@nvidia.com>
Link: https://lore.kernel.org/r/1646191769-17761-1-git-send-email-baowen.zheng@corigine.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

net/sched/act_api.c

@@ -1446,6 +1446,8 @@ int tcf_action_init(struct net *net, struct tcf_proto *tp, struct nlattr *nla,
 				continue;
 			if (skip_sw != tc_act_skip_sw(act->tcfa_flags) ||
 			    skip_hw != tc_act_skip_hw(act->tcfa_flags)) {
+				NL_SET_ERR_MSG(extack,
+					       "Mismatch between action and filter offload flags");
 				err = -EINVAL;
 				goto err;
 			}