[SPARK-21064][CORE][TEST] Fix the default value bug in NettyBlockTransferServiceSuite

## What changes were proposed in this pull request?

The default value for `spark.port.maxRetries` is 100,
but we use 10 in the suite file.
So we change it to 100 to avoid test failure.

## How was this patch tested?
No test

Author: DjvuLee <lihu@bytedance.com>

Closes #18280 from djvulee/NettyTestBug.

core/src/test/scala/org/apache/spark/network/netty/NettyBlockTransferServiceSuite.scala

@@ -80,7 +80,8 @@ class NettyBlockTransferServiceSuite
   private def verifyServicePort(expectedPort: Int, actualPort: Int): Unit = {
     actualPort should be >= expectedPort
     // avoid testing equality in case of simultaneous tests
-    actualPort should be <= (expectedPort + 10)
+    // the default value for `spark.port.maxRetries` is 100 under test
+    actualPort should be <= (expectedPort + 100)
   }
 
   private def createService(port: Int): NettyBlockTransferService = {