*: Port Christians tweaks for 32-bit route tags

Port over Christian's tweaks from his port of my commit widening the
route-tag field width to 32-bit.  Commit dc9ffce8786844
 "*: Consistently support 32-bit route tags".

with "changes which make this actually useful for all the daemons".

This is missing the zebra route-map changes.
diff --git a/zebra/zserv.c b/zebra/zserv.c
index 2c0c5b4..a96bcb1 100644
--- a/zebra/zserv.c
+++ b/zebra/zserv.c
@@ -986,7 +986,9 @@
   /* Tag */
   if (CHECK_FLAG (message, ZAPI_MESSAGE_TAG))
     rib->tag = stream_getl (s);
-
+  else
+    rib->tag = 0;
+  
   /* Table */
   rib->table=zebrad.rtm_table_default;
   ret = rib_add_ipv4_multipath (&p, rib, safi);
@@ -1222,7 +1224,9 @@
   /* Tag */
   if (CHECK_FLAG (message, ZAPI_MESSAGE_TAG))
     rib->tag = stream_getl (s);
-
+  else
+    rib->tag = 0;
+  
   /* Table */
   rib->table=zebrad.rtm_table_default;
   ret = rib_add_ipv6_multipath (&p, rib, safi);