change the log description to cover more case

The configService not only includes the default configuration.

Change-Id: Ieeb21b492fd1025676f0d302a7c65499117febec
diff --git a/src/main/java/net/onrc/onos/apps/proxyarp/ProxyArpManager.java b/src/main/java/net/onrc/onos/apps/proxyarp/ProxyArpManager.java
index 8410b43..cfdd9c1 100644
--- a/src/main/java/net/onrc/onos/apps/proxyarp/ProxyArpManager.java
+++ b/src/main/java/net/onrc/onos/apps/proxyarp/ProxyArpManager.java
@@ -533,8 +533,8 @@
             // TODO handle the case where the controller needs to send an ARP
             // request but there's not IP configuration. In this case the
             // request should be broadcast out all edge ports in the network.
-            log.warn("Sending ARP requests with default configuration "
-                    + "not supported");
+            log.warn("Cannot send ARP: there is no outgoing interface in the "
+                    + "configuration");
             return;
         }