*: 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/bgpd/bgp_attr.h b/bgpd/bgp_attr.h
index 0bbb912..0cd0b77 100644
--- a/bgpd/bgp_attr.h
+++ b/bgpd/bgp_attr.h
@@ -94,7 +94,7 @@
   struct bgp_attr_encap_subtlv *encap_subtlvs;		/* rfc5512 */
 
   /* route tag */
-  u_short tag;
+  route_tag_t tag;
 };
 
 /* BGP core attribute structure. */