cls: add rtnl_u32_get_classid() API

[thaller@redhat.com: modified patch to use rtnl_tc_data_peek()]

http://lists.infradead.org/pipermail/libnl/2015-March/001841.html

Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: Thomas Haller <thaller@redhat.com>
diff --git a/libnl-route-3.sym b/libnl-route-3.sym
index 9093149..139a499 100644
--- a/libnl-route-3.sym
+++ b/libnl-route-3.sym
@@ -864,4 +864,5 @@
 	rtnl_tc_str2stat;
 	rtnl_u32_add_mark;
 	rtnl_u32_del_mark;
+	rtnl_u32_get_classid;
 } libnl_3;