[NET_SCHED]: Add #ifdef CONFIG_NET_EMATCH in net/sched/cls_flow.c (latest git broken build)

The 2.6 latest git build was broken when using the following
configuration options:
CONFIG_NET_EMATCH=n
CONFIG_NET_CLS_FLOW=y

with the following error:
net/sched/cls_flow.c: In function 'flow_dump':
net/sched/cls_flow.c:598: error: 'struct tcf_ematch_tree' has no
member named 'hdr'
make[2]: *** [net/sched/cls_flow.o] Error 1
make[1]: *** [net/sched] Error 2
make: *** [net] Error 2


see the recent post by Li Zefan:
  http://www.spinics.net/lists/netdev/msg54434.html

The reason for this crash is that struct tcf_ematch_tree
(net/pkt_cls.h) is empty when CONFIG_NET_EMATCH is not defined.

When CONFIG_NET_EMATCH is defined, the tcf_ematch_tree structure
indeed holds a struct tcf_ematch_tree_hdr (hdr) as flow_dump()
expects.

This patch adds #ifdef CONFIG_NET_EMATCH in flow_dump to avoid this.

Signed-off-by: Rami Rosen <ramirose@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sched/cls_flow.c

@@ -594,11 +594,11 @@ static int flow_dump(struct tcf_proto *tp, unsigned long fh,
 
 	if (tcf_exts_dump(skb, &f->exts, &flow_ext_map) < 0)
 		goto nla_put_failure;
-
+#ifdef CONFIG_NET_EMATCH
 	if (f->ematches.hdr.nmatches &&
 	    tcf_em_tree_dump(skb, &f->ematches, TCA_FLOW_EMATCHES) < 0)
 		goto nla_put_failure;
-
+#endif
 	nla_nest_end(skb, nest);
 
 	if (tcf_exts_dump_stats(skb, &f->exts, &flow_ext_map) < 0)