ospf: Fix OSPF API and ospf-te LSA refreshers to match recent API change

* ospf_apiserver.{c,h}: (ospf_apiserver_lsa_refresher) refreshers must now
  return the refreshed LSA.
* ospf_te.{c,h}: (ospf_mpls_te_lsa_refresh) ditto
* ospf_api.c: trivial compiler warning fix
diff --git a/ospfd/ospf_apiserver.c b/ospfd/ospf_apiserver.c
index 15fd2e5..2a9003b 100644
--- a/ospfd/ospf_apiserver.c
+++ b/ospfd/ospf_apiserver.c
@@ -1831,7 +1831,7 @@
 
 /* Periodically refresh opaque LSAs so that they do not expire in
    other routers. */
-void
+struct ospf_lsa *
 ospf_apiserver_lsa_refresher (struct ospf_lsa *lsa)
 {
   struct ospf_apiserver *apiserv;
@@ -1904,7 +1904,7 @@
     }
 
 out:
-  return;
+  return new;
 }