ospf6d: address more trivial compiler warnings

* ospf6_main.c: include required headers
* ospf6_asbr.h: idem
* ospf6_spf.c
  * ospf6_spf_install(): remove unused variables
diff --git a/ospf6d/ospf6_spf.c b/ospf6d/ospf6_spf.c
index cb54961..beb6d7f 100644
--- a/ospf6d/ospf6_spf.c
+++ b/ospf6d/ospf6_spf.c
@@ -282,8 +282,7 @@
 {
   struct ospf6_route *route;
   int i, j;
-  struct ospf6_vertex *prev, *w;
-  struct listnode *node, *nnode;
+  struct ospf6_vertex *prev;
 
   if (IS_OSPF6_DEBUG_SPF (PROCESS))
     zlog_debug ("SPF install %s hops %d cost %d",