ospfd: Make "Packet ... received on wrong link" conditional on debug

* ospf_packet.c: make this message conditional on 'debug ospf event', as it
  be easily triggered with, e.g., multiple subnets sharing same physical
  network. E.g, see bug #532.
diff --git a/ospfd/ospf_packet.c b/ospfd/ospf_packet.c
index effef39..8f61ed1 100644
--- a/ospfd/ospf_packet.c
+++ b/ospfd/ospf_packet.c
@@ -2425,8 +2425,9 @@
    */
   else if (oi->ifp != ifp)
     {
-      zlog_warn ("Packet from [%s] received on wrong link %s",
-                 inet_ntoa (iph->ip_src), ifp->name); 
+      if (IS_DEBUG_OSPF_EVENT)
+        zlog_warn ("Packet from [%s] received on wrong link %s",
+                   inet_ntoa (iph->ip_src), ifp->name); 
       return 0;
     }
   else if (oi->state == ISM_Down)