HDFS-16391. Avoid evaluation of LOG.debug statement in NameNodeHeartbeatService (#3820)

(cherry picked from commit 8d251bd629c2db33f03c80e93c7e54fceedbfbe6)

hadoop-hdfs-project/hadoop-hdfs-rbf/src/main/java/org/apache/hadoop/hdfs/server/federation/router/NamenodeHeartbeatService.java

@@ -221,12 +221,16 @@ public class NamenodeHeartbeatService extends PeriodicService {
       LOG.error("Namenode is not operational: {}", getNamenodeDesc());
     } else if (report.haStateValid()) {
       // block and HA status available
-      LOG.debug("Received service state: {} from HA namenode: {}",
-          report.getState(), getNamenodeDesc());
+      if (LOG.isDebugEnabled()) {
+        LOG.debug("Received service state: {} from HA namenode: {}",
+            report.getState(), getNamenodeDesc());
+      }
     } else if (localTarget == null) {
       // block info available, HA status not expected
-      LOG.debug(
-          "Reporting non-HA namenode as operational: " + getNamenodeDesc());
+      if (LOG.isDebugEnabled()) {
+        LOG.debug(
+            "Reporting non-HA namenode as operational: {}", getNamenodeDesc());
+      }
     } else {
       // block info available, HA status should be available, but was not
       // fetched do nothing and let the current state stand