ospf6d: convert LSDB to use route_node, improve performance

the performance in the presence of a large number of LSAs. I also verified
that the performance improvements stayed in the presence of a large number
of peers (I tested upto 128).

Signed-off-by: Dinesh G Dutt <ddutt at cumulusnetworks.com>
Reviewed-by: Scott Feldman <sfeldma at cumulusnetworks.com>Summary:
Reviewed-by: James Li <jli at cumulusnetworks.com>
Signed-off-by: David Lamparter <equinox@opensourcerouting.org>
diff --git a/ospf6d/ospf6_lsa.h b/ospf6d/ospf6_lsa.h
index f10ee67..998599b 100644
--- a/ospf6d/ospf6_lsa.h
+++ b/ospf6d/ospf6_lsa.h
@@ -114,8 +114,7 @@
 {
   char              name[64];   /* dump string */
 
-  struct ospf6_lsa *prev;
-  struct ospf6_lsa *next;
+  struct route_node *rn;
 
   unsigned char     lock;           /* reference counter */
   unsigned char     flag;           /* special meaning (e.g. floodback) */