HDFS-15936.Solve SocketTimeoutException#sendPacket() does not record SocketTimeout exception. (#2836)

Co-authored-by: zhujianghua <zhujianghua@zhujianghuadeMacBook-Pro.local>
Reviewed-by: cxorm <lianp964@gmail.com>
Reviewed-by: Viraj Jasani <vjasani@apache.org>

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/BlockSender.java

@@ -632,6 +632,7 @@ class BlockSender implements java.io.Closeable {
          * 
          * Reporting of this case is done in DataXceiver#run
          */
+        LOG.warn("Sending packets timed out.", e);
       } else {
         /* Exception while writing to the client. Connection closure from
          * the other end is mostly the case and we do not care much about