[#2925] Bug fix for NormalMemoryRegionCache overbooked for PoolThreadCache

Motivation:

When create NormalMemoryRegionCache for PoolThreadCache, we overbooked
cache array size. This means unnecessary overhead for thread local cache
as we will create multi cache enties for each element in cache array.

Modifications:

change:
int arraySize = Math.max(1, max / area.pageSize);
to:
int arraySize = Math.max(1, log2(max / area.pageSize) + 1);

Result:

Now arraySize won't introduce unnecessary overhead.

 Changes to be committed:
	modified:   buffer/src/main/java/io/netty/buffer/PoolThreadCache.java

buffer/src/main/java/io/netty/buffer/PoolThreadCache.java

@@ -129,7 +129,7 @@ final class PoolThreadCache {
             int cacheSize, int maxCachedBufferCapacity, PoolArena<T> area) {
         if (cacheSize > 0) {
             int max = Math.min(area.chunkSize, maxCachedBufferCapacity);
-            int arraySize = Math.max(1, max / area.pageSize);
+            int arraySize = Math.max(1, log2(max / area.pageSize) + 1);
 
             @SuppressWarnings("unchecked")
             NormalMemoryRegionCache<T>[] cache = new NormalMemoryRegionCache[arraySize];