minor trace logging fixes

Change-Id: I9229aa551532470b0581f2f17acb0be4793c24a7
diff --git a/core/net/src/main/java/org/onosproject/net/link/impl/LinkManager.java b/core/net/src/main/java/org/onosproject/net/link/impl/LinkManager.java
index 1d8ca4d..64bf8b3 100644
--- a/core/net/src/main/java/org/onosproject/net/link/impl/LinkManager.java
+++ b/core/net/src/main/java/org/onosproject/net/link/impl/LinkManager.java
@@ -260,7 +260,7 @@
             if (isAllowed(cfg) && isAllowed(cfgTwo)) {
                 return BasicLinkOperator.combine(cfg, linkDescription);
             } else {
-                log.trace("Link " + linkDescription.toString() + " is not allowed");
+                log.trace("Link {} is not allowed", linkDescription);
                 return null;
             }
         }