ISPN-8655 Off Heap Size Estimation rounds improperly

* Make sure to round up to 16 properly
* Added tests

core/src/main/java/org/infinispan/container/offheap/UnpooledOffHeapMemoryAllocator.java

@@ -72,6 +72,6 @@ public long getAllocatedAmount() {
     */
    public static long estimateSizeOverhead(long size) {
       // We take 8 and add the number provided and then round up to 16 (& operator has higher precedence than +)
-      return (size + 8 + 15) & ~0x15;
+      return (size + 8 + 15) & ~15;
    }
 }

core/src/test/java/org/infinispan/container/offheap/UnpooledOffHeapMemoryAllocatorTest.java

@@ -0,0 +1,33 @@
+package org.infinispan.container.offheap;
+
+import static org.testng.AssertJUnit.assertEquals;
+
+import org.testng.annotations.DataProvider;
+import org.testng.annotations.Test;
+
+/**
+ * @author wburns
+ * @since 9.0
+ */
+@Test(groups = "functional", testName = "container.offheap.UnpooledOffHeapMemoryAllocatorTest")
+public class UnpooledOffHeapMemoryAllocatorTest {
+
+   @DataProvider(name = "roundings")
+   Object[][] roundings() {
+      return new Object[][] {
+            { 2, 16 },
+            { 14, 32 },
+            { 23, 32 },
+            { 32, 48 },
+            { 123, 144 },
+            { 43, 64 },
+            { 73, 96 },
+      };
+   }
+
+   @Test(dataProvider = "roundings")
+   public void testRoundings(long original, long expected) {
+      // The estimate adds 8 and rounds up to 16
+      assertEquals(expected, UnpooledOffHeapMemoryAllocator.estimateSizeOverhead(original));
+   }
+}