rib: make log messages of AutoPrefixPropagator more accurate

Change-Id: Ieadfb95cd97b6f4ad0397d927ab31b21da3aa431
ref: #3774
diff --git a/rib/auto-prefix-propagator.cpp b/rib/auto-prefix-propagator.cpp
index edd5763..d3e9e86 100644
--- a/rib/auto-prefix-propagator.cpp
+++ b/rib/auto-prefix-propagator.cpp
@@ -178,9 +178,15 @@
   auto entryIt = m_propagatedEntries.find(propagateParameters.parameters.getName());
   if (entryIt != m_propagatedEntries.end()) {
     // in addition to PROPAGATED and PROPAGATE_FAIL, the state may also be NEW,
-    // if its propagation was suspended because there was no connectivity to the Hub.
-    NFD_LOG_INFO("prefix has already been propagated: "
-                 << propagateParameters.parameters.getName());
+    // if there is no hub connected to propagate this prefix.
+    if (entryIt->second.isNew()) {
+      NFD_LOG_INFO("no hub connected to propagate "
+                   << propagateParameters.parameters.getName());
+    }
+    else {
+      NFD_LOG_INFO("prefix has already been propagated: "
+                   << propagateParameters.parameters.getName());
+    }
     return;
   }