netfilter: ipset: Introduce extensions to elements in the core

Introduce extensions to elements in the core and prepare timeout as
the first one.

This patch also modifies the em_ipset classifier to use the new
extension struct layout.

Signed-off-by: Jozsef Kadlecsik <kadlec@blackhole.kfki.hu>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
diff --git a/net/sched/em_ipset.c b/net/sched/em_ipset.c
index 3130320..938b7cb 100644
--- a/net/sched/em_ipset.c
+++ b/net/sched/em_ipset.c
@@ -83,7 +83,7 @@
 	opt.dim = set->dim;
 	opt.flags = set->flags;
 	opt.cmdflags = 0;
-	opt.timeout = ~0u;
+	opt.ext.timeout = ~0u;
 
 	network_offset = skb_network_offset(skb);
 	skb_pull(skb, network_offset);