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_flow.c

@@ -455,6 +455,7 @@ static int flow_change(struct net *net, struct sk_buff *in_skb,
 
 		f->handle = handle;
 		f->mask	  = ~0U;
+		tcf_exts_init(&f->exts);
 
 		get_random_bytes(&f->hashrnd, 4);
 		f->perturb_timer.function = flow_perturbation;