zebra: add structure to hold per-prefix state in RIB

Add the rib_dest_t structure to hold per-prefix state in the routing
information base. This gives us an appropriate place to maintain the
queueing state of a route_node. Queuing state was previously being
stored on the first rib in the list of ribs hanging off the
route_node.

  * zebra/rib.h

    - Add new structure rib_dest_t.

    - Remove the rn_status field from 'struct rib', it is no longer
      required.

    - Add macros (RNODE_FOREACH_RIB, RNODE_FOREACH_RIB_SAFE) for
      walking all 'struct ribs' corresponding to a route_node. These
      hide the fact that there is an intermediate rib_dest_t
      structure.

    - Add a few utility inlines to go between a rib_dest_t and
      associated structures.

  * zebra/zebra_rib.c

    - rib_link()/rib_unlink()

      Tweak for new behavior, where the 'info' pointer of a route_node
      points to a rib_dest_t. The list of ribs for a prefix now hangs
      off of the dest.

      Change the way we ref count route_nodes. We now hold a single
      ref count on a route_node if there is a corresponding
      rib_dest_t.

    - Maintain the queuing state of a route_node on the flags field of
      the rib_dest_t.

    - Add the rib_gc_dest() function, which deletes a rib_dest_t if it
      is no longer required. A rib_dest_t can be deleted iff there are
      no struct ribs hanging off of it.

    - Call rib_gc_dest() any time we unlink a rib from the
      rib_dest_t. Currently we only need to call it once, just before
      we return from rib_process().

  * zebra/{redistribute,zebra_rib,zebra_snmp,zebra_vty}.c

    Use new macros to walk over route_node ribs.

  * lib/memtypes.c

    Add memory type for rib_dest_t.

Signed-off-by: Avneesh Sachdev <avneesh@opensourcerouting.org>
Signed-off-by: David Lamparter <equinox@opensourcerouting.org>
diff --git a/zebra/zebra_vty.c b/zebra/zebra_vty.c
index 743c13f..d07b09c 100644
--- a/zebra/zebra_vty.c
+++ b/zebra/zebra_vty.c
@@ -535,7 +535,7 @@
   struct rib *rib;
   struct nexthop *nexthop;
 
-  for (rib = rn->info; rib; rib = rib->next)
+  RNODE_FOREACH_RIB (rn, rib)
     {
       vty_out (vty, "Routing entry for %s/%d%s", 
 	       inet_ntoa (rn->p.u.prefix4), rn->p.prefixlen,
@@ -822,7 +822,7 @@
 
   /* Show all IPv4 routes. */
   for (rn = route_top (table); rn; rn = route_next (rn))
-    for (rib = rn->info; rib; rib = rib->next)
+    RNODE_FOREACH_RIB (rn, rib)
       {
 	if (first)
 	  {
@@ -863,7 +863,7 @@
 
   /* Show matched type IPv4 routes. */
   for (rn = route_top (table); rn; rn = route_next (rn))
-    for (rib = rn->info; rib; rib = rib->next)
+    RNODE_FOREACH_RIB (rn, rib)
       if (prefix_match (&p, &rn->p))
 	{
 	  if (first)
@@ -896,7 +896,7 @@
 
   /* Show matched type IPv4 routes. */
   for (rn = route_top (table); rn; rn = route_next (rn))
-    for (rib = rn->info; rib; rib = rib->next)
+    RNODE_FOREACH_RIB (rn, rib)
       {
 	addr = ntohl (rn->p.u.prefix4.s_addr);
 
@@ -942,7 +942,7 @@
 
   /* Show matched type IPv4 routes. */
   for (rn = route_top (table); rn; rn = route_next (rn))
-    for (rib = rn->info; rib; rib = rib->next)
+    RNODE_FOREACH_RIB (rn, rib)
       if (rib->type == type)
 	{
 	  if (first)
@@ -1046,7 +1046,7 @@
   memset (&rib_cnt, 0, sizeof(rib_cnt));
   memset (&fib_cnt, 0, sizeof(fib_cnt));
   for (rn = route_top (table); rn; rn = route_next (rn))
-    for (rib = rn->info; rib; rib = rib->next)
+    RNODE_FOREACH_RIB (rn, rib)
       for (nexthop = rib->nexthop; nexthop; nexthop = nexthop->next)
         {
 	  rib_cnt[ZEBRA_ROUTE_TOTAL]++;
@@ -1219,7 +1219,7 @@
 
   /* Show all IPv4 routes. */
   for (rn = route_top (table); rn; rn = route_next (rn))
-    for (rib = rn->info; rib; rib = rib->next)
+    RNODE_FOREACH_RIB (rn, rib)
       {
        if (first)
          {
@@ -1546,7 +1546,7 @@
   struct nexthop *nexthop;
   char buf[BUFSIZ];
 
-  for (rib = rn->info; rib; rib = rib->next)
+  RNODE_FOREACH_RIB (rn, rib)
     {
       vty_out (vty, "Routing entry for %s/%d%s", 
 	       inet_ntop (AF_INET6, &rn->p.u.prefix6, buf, BUFSIZ),
@@ -1795,7 +1795,7 @@
 
   /* Show all IPv6 route. */
   for (rn = route_top (table); rn; rn = route_next (rn))
-    for (rib = rn->info; rib; rib = rib->next)
+    RNODE_FOREACH_RIB (rn, rib)
       {
 	if (first)
 	  {
@@ -1836,7 +1836,7 @@
 
   /* Show matched type IPv6 routes. */
   for (rn = route_top (table); rn; rn = route_next (rn))
-    for (rib = rn->info; rib; rib = rib->next)
+    RNODE_FOREACH_RIB (rn, rib)
       if (prefix_match (&p, &rn->p))
 	{
 	  if (first)
@@ -1876,7 +1876,7 @@
 
   /* Show matched type IPv6 routes. */
   for (rn = route_top (table); rn; rn = route_next (rn))
-    for (rib = rn->info; rib; rib = rib->next)
+    RNODE_FOREACH_RIB (rn, rib)
       if (rib->type == type)
 	{
 	  if (first)
@@ -2008,7 +2008,7 @@
 
   /* Show all IPv6 route. */
   for (rn = route_top (table); rn; rn = route_next (rn))
-    for (rib = rn->info; rib; rib = rib->next)
+    RNODE_FOREACH_RIB (rn, rib)
       {
        if (first)
          {