Fix IllegalArgumentException when release a wrapped ByteBuffer on Java9

Motivation:

Unsafe.invokeCleaner(...) checks if the passed in ByteBuffer is a slice or duplicate and if so throws an IllegalArgumentException on Java9. We need to ensure we never try to free a ByteBuffer that was provided by the user directly as we not know if its a slice / duplicate or not.

Modifications:

Never try to free a ByteBuffer that was passed into UnpooledUnsafeDirectByteBuf constructor by an user (via Unpooled.wrappedBuffer(....)).

Result:

Build passes again on Java9

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

@@ -74,7 +74,16 @@ public class UnpooledUnsafeDirectByteBuf extends AbstractReferenceCountedByteBuf
      * @param maxCapacity the maximum capacity of the underlying direct buffer
      */
     protected UnpooledUnsafeDirectByteBuf(ByteBufAllocator alloc, ByteBuffer initialBuffer, int maxCapacity) {
-        this(alloc, initialBuffer, maxCapacity, true);
+        // We never try to free the buffer if it was provided by the end-user as we not know if this is an duplicate or
+        // an slice. This is done to prevent an IllegalArgumentException when using Java9 as Unsafe.invokeCleaner(...)
+        // will check if the given buffer is either an duplicate or slice and in this case throw an
+        // IllegalArgumentException.
+        //
+        // See http://hg.openjdk.java.net/jdk9/hs-demo/jdk/file/0d2ab72ba600/src/jdk.unsupported/share/classes/
+        // sun/misc/Unsafe.java#l1250
+        //
+        // We also call slice() explicitly here to preserve behaviour with previous netty releases.
+        this(alloc, initialBuffer.slice(), maxCapacity, false);
     }
 
     UnpooledUnsafeDirectByteBuf(ByteBufAllocator alloc, ByteBuffer initialBuffer, int maxCapacity, boolean doFree) {
@@ -100,7 +109,7 @@ public class UnpooledUnsafeDirectByteBuf extends AbstractReferenceCountedByteBuf
 
         this.alloc = alloc;
         doNotFree = !doFree;
-        setByteBuffer(initialBuffer.slice().order(ByteOrder.BIG_ENDIAN), false);
+        setByteBuffer(initialBuffer.order(ByteOrder.BIG_ENDIAN), false);
         writerIndex(initialCapacity);
     }