[NET_SCHED]: act_api: qdisc internal reclassify support

The behaviour of NET_CLS_POLICE for TC_POLICE_RECLASSIFY was to return
it to the qdisc, which could handle it internally or ignore it. With
NET_CLS_ACT however, tc_classify starts over at the first classifier
and never returns it to the qdisc. This makes it impossible to support
qdisc-internal reclassification, which in turn makes it impossible to
remove the old NET_CLS_POLICE code without breaking compatibility since
we have two qdiscs (CBQ and ATM) that support this.

This patch adds a tc_classify_compat function that handles
reclassification the old way and changes CBQ and ATM to use it.

This again is of course not fully backwards compatible with the previous
NET_CLS_ACT behaviour. Unfortunately there is no way to fully maintain
compatibility *and* support qdisc internal reclassification with
NET_CLS_ACT, but this seems like the better choice over keeping the two
incompatible options around forever.

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/pkt_sched.h

@@ -89,8 +89,10 @@ static inline void qdisc_run(struct net_device *dev)
 		__qdisc_run(dev);
 }
 
+extern int tc_classify_compat(struct sk_buff *skb, struct tcf_proto *tp,
+			      struct tcf_result *res);
 extern int tc_classify(struct sk_buff *skb, struct tcf_proto *tp,
-	struct tcf_result *res);
+		       struct tcf_result *res);
 
 /* Calculate maximal size of packet seen by hard_start_xmit
    routine of this device.

include/net/sch_generic.h

@@ -290,7 +290,7 @@ static inline int qdisc_reshape_fail(struct sk_buff *skb, struct Qdisc *sch)
 {
 	sch->qstats.drops++;
 
-#ifdef CONFIG_NET_CLS_POLICE
+#if defined(CONFIG_NET_CLS_ACT) || defined(CONFIG_NET_CLS_POLICE)
 	if (sch->reshape_fail == NULL || sch->reshape_fail(skb, sch))
 		goto drop;