net_sched: act: use standard struct list_head

Currently actions are chained by a singly linked list,
therefore it is a bit hard to add and remove a specific
entry. Convert it to struct list_head so that in the
latter patch we can remove an action without finding
its head.

Cc: Jamal Hadi Salim <jhs@mojatatu.com>
Cc: David S. Miller <davem@davemloft.net>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: Jamal Hadi Salim <jhs@mojatatu.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sched/cls_u32.c

@@ -646,6 +646,7 @@ static int u32_change(struct net *net, struct sk_buff *in_skb,
 	n->ht_up = ht;
 	n->handle = handle;
 	n->fshift = s->hmask ? ffs(ntohl(s->hmask)) - 1 : 0;
+	tcf_exts_init(&n->exts);
 
 #ifdef CONFIG_CLS_U32_MARK
 	if (tb[TCA_U32_MARK]) {