net/sched: act_api: add specific EXT_WARN_MSG for tc action

In my previous commit 0349b8779cc9 ("sched: add new attr TCA_EXT_WARN_MSG
to report tc extact message") I didn't notice the tc action use different
enum with filter. So we can't use TCA_EXT_WARN_MSG directly for tc action.
Let's add a TCA_ROOT_EXT_WARN_MSG for tc action specifically and put this
param before going to the TCA_ACT_TAB nest.

Fixes: 0349b8779cc9 ("sched: add new attr TCA_EXT_WARN_MSG to report tc extact message")
Signed-off-by: Hangbin Liu <[e-mail]>
Acked-by: Jamal Hadi Salim <[e-mail]>
Signed-off-by: Jakub Kicinski <[e-mail]>

include/uapi/linux/rtnetlink.h

···
 	TCA_ROOT_FLAGS,
 	TCA_ROOT_COUNT,
 	TCA_ROOT_TIME_DELTA, /* in msecs */
+	TCA_ROOT_EXT_WARN_MSG,
 	__TCA_ROOT_MAX,
 #define	TCA_ROOT_MAX (__TCA_ROOT_MAX - 1)
 };

net/sched/act_api.c

···
 	t->tca__pad1 = 0;
 	t->tca__pad2 = 0;
 
+	if (extack && extack->_msg &&
+	    nla_put_string(skb, TCA_ROOT_EXT_WARN_MSG, extack->_msg))
+		goto out_nlmsg_trim;
+
 	nest = nla_nest_start_noflag(skb, TCA_ACT_TAB);
 	if (!nest)
 		goto out_nlmsg_trim;
···
 		goto out_nlmsg_trim;
 
 	nla_nest_end(skb, nest);
-
-	if (extack && extack->_msg &&
-	    nla_put_string(skb, TCA_EXT_WARN_MSG, extack->_msg))
-		goto out_nlmsg_trim;
 
 	nlh->nlmsg_len = skb_tail_pointer(skb) - b;