*: Widen width of Zserv routing tag field.

* lib/zebra.h: Introduce a route_tag_t type for route tags generally,
  and make it 4 bytes wide - so it can directly hold things like an ASN, or
  the OSPF ASE-LSA tag.
* zebra/rib.h: Use route_tag_t instead of u_short.
* *: Update 'u_short (*)?(tag|tmp)' to use route_tag_t instead of u_short.
  Update stream_{get,put} to l instead of w.
* ospf_zebra.c: (ospf_zebra_add) test OSPF tag within range of ROUTE_TAG_MAX.
diff --git a/ospfd/ospf_asbr.c b/ospfd/ospf_asbr.c
index 4b53690..0a411e4 100644
--- a/ospfd/ospf_asbr.c
+++ b/ospfd/ospf_asbr.c
@@ -136,7 +136,7 @@
 struct external_info *
 ospf_external_info_add (u_char type, struct prefix_ipv4 p,
 			ifindex_t ifindex, struct in_addr nexthop,
-                        u_short tag)
+                        route_tag_t tag)
 {
   struct external_info *new;
   struct route_node *rn;