[MINOR][NETWORK][TEST] Fix TransportFrameDecoderSuite to use ByteBuf …

…instead of ByteBuffer

## What changes were proposed in this pull request?

`fireChannelRead` expects `io.netty.buffer.ByteBuf`.I checked that this is the only place which misuse `java.nio.ByteBuffer` in `network` module.

## How was this patch tested?

Pass the Jenkins with the existing tests.

Closes apache#23442 from dongjoon-hyun/SPARK-NETWORK-COMMON.

Authored-by: Dongjoon Hyun <dongjoon@apache.org>
Signed-off-by: Dongjoon Hyun <dongjoon@apache.org>

common/network-common/src/test/java/org/apache/spark/network/util/TransportFrameDecoderSuite.java

@@ -17,7 +17,6 @@
 
 package org.apache.spark.network.util;
 
-import java.nio.ByteBuffer;
 import java.util.ArrayList;
 import java.util.List;
 import java.util.Random;
@@ -69,7 +68,7 @@ public void testInterception() throws Exception {
       decoder.channelRead(ctx, len);
       decoder.channelRead(ctx, dataBuf);
       verify(interceptor, times(interceptedReads)).handle(any(ByteBuf.class));
-      verify(ctx).fireChannelRead(any(ByteBuffer.class));
+      verify(ctx).fireChannelRead(any(ByteBuf.class));
       assertEquals(0, len.refCnt());
       assertEquals(0, dataBuf.refCnt());
     } finally {