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_asbr.h b/ospf6d/ospf6_asbr.h
index 7166aa3..72644df 100644
--- a/ospf6d/ospf6_asbr.h
+++ b/ospf6d/ospf6_asbr.h
@@ -22,6 +22,13 @@
 #ifndef OSPF6_ASBR_H
 #define OSPF6_ASBR_H
 
+/* for struct ospf6_prefix */
+#include "ospf6_proto.h"
+/* for struct ospf6_lsa */
+#include "ospf6_lsa.h"
+/* for struct ospf6_route */
+#include "ospf6_route.h"
+
 /* Debug option */
 extern unsigned char conf_debug_ospf6_asbr;
 #define OSPF6_DEBUG_ASBR_ON() \