[NET_SCHED]: Constify struct tcf_ext_map

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/sched/cls_basic.c b/net/sched/cls_basic.c
index bfb4342..956915c 100644
--- a/net/sched/cls_basic.c
+++ b/net/sched/cls_basic.c
@@ -35,7 +35,7 @@
 	struct list_head	link;
 };
 
-static struct tcf_ext_map basic_ext_map = {
+static const struct tcf_ext_map basic_ext_map = {
 	.action = TCA_BASIC_ACT,
 	.police = TCA_BASIC_POLICE
 };