[apache#1161] improvement(netty): Reduce the data copy when accessing…

… data buffer len (apache#1162)

### What changes were proposed in this pull request?

If we use the off heap memory and then we use the method `getData`, we will copy the off heap memory to heap data memory. So we should avoid using it in the Netty mode.

### Why are the changes needed?

Fix: apache#1161

### Does this PR introduce _any_ user-facing change?

No.

### How was this patch tested?
Code Review

server/src/main/java/org/apache/uniffle/server/netty/ShuffleServerNettyHandler.java

@@ -442,8 +442,9 @@ public void handleGetLocalShuffleData(TransportClient client, GetLocalShuffleDat
  length);
  long readTime = System.currentTimeMillis() - start;
  ShuffleServerMetrics.counterTotalReadTime.inc(readTime);
- ShuffleServerMetrics.counterTotalReadDataSize.inc(sdr.getData().length);
- ShuffleServerMetrics.counterTotalReadLocalDataFileSize.inc(sdr.getData().length);
+ int dataLength = sdr.getDataBuffer().remaining();
+ ShuffleServerMetrics.counterTotalReadDataSize.inc(dataLength);
+ ShuffleServerMetrics.counterTotalReadLocalDataFileSize.inc(dataLength);
  shuffleServer
  .getNettyMetrics()
  .recordProcessTime(GetLocalShuffleDataRequest.class.getName(), readTime);

storage/src/main/java/org/apache/uniffle/storage/handler/impl/LocalFileClientReadHandler.java

@@ -153,10 +153,10 @@ public ShuffleDataResult readShuffleData(ShuffleDataSegment shuffleDataSegment)
  + " due to "
  + e.getMessage());
  }
- if (result.getData().length != expectedLength) {
+ if (result.getDataBuffer().remaining() != expectedLength) {
  throw new RssException(
  "Wrong data length expect "
- + result.getData().length
+ + result.getDataBuffer().remaining()
  + " but actual is "
  + expectedLength);
  }