*: 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/lib/zebra.h b/lib/zebra.h
index a75eb6d..a405d46 100644
--- a/lib/zebra.h
+++ b/lib/zebra.h
@@ -535,4 +535,7 @@
 /* VRF ID type. */
 typedef u_int16_t vrf_id_t;
 
+typedef uint32_t route_tag_t;
+#define ROUTE_TAG_MAX UINT32_MAX
+
 #endif /* _ZEBRA_H */