Use threadsafe setter on Atomic Updaters

Motivation:
The documentation for field updates says:

> Note that the guarantees of the {@code compareAndSet}
> method in this class are weaker than in other atomic classes.
> Because this class cannot ensure that all uses of the field
> are appropriate for purposes of atomic access, it can
> guarantee atomicity only with respect to other invocations of
> {@code compareAndSet} and {@code set} on the same updater.

This implies that volatiles shouldn't use normal assignment; the
updater should set them.

Modifications:
Use setter for field updaters that make use of compareAndSet.

Result:
Concurrency compliant code

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

@@ -30,10 +30,11 @@ public abstract class AbstractReferenceCountedByteBuf extends AbstractByteBuf {
     private static final AtomicIntegerFieldUpdater<AbstractReferenceCountedByteBuf> refCntUpdater =
             AtomicIntegerFieldUpdater.newUpdater(AbstractReferenceCountedByteBuf.class, "refCnt");
 
-    private volatile int refCnt = 1;
+    private volatile int refCnt;
 
     protected AbstractReferenceCountedByteBuf(int maxCapacity) {
         super(maxCapacity);
+        refCntUpdater.set(this, 1);
     }
 
     @Override
@@ -45,7 +46,7 @@ public abstract class AbstractReferenceCountedByteBuf extends AbstractByteBuf {
      * An unsafe operation intended for use by a subclass that sets the reference count of the buffer directly
      */
     protected final void setRefCnt(int refCnt) {
-        this.refCnt = refCnt;
+        refCntUpdater.set(this, refCnt);
     }
 
     @Override

common/src/main/java/io/netty/util/AbstractReferenceCounted.java

@@ -38,7 +38,7 @@ public abstract class AbstractReferenceCounted implements ReferenceCounted {
      * An unsafe operation intended for use by a subclass that sets the reference count of the buffer directly
      */
     protected final void setRefCnt(int refCnt) {
-        this.refCnt = refCnt;
+        refCntUpdater.set(this, refCnt);
     }
 
     @Override

common/src/main/java/io/netty/util/HashedWheelTimer.java

@@ -97,8 +97,8 @@ public class HashedWheelTimer implements Timer {
     public static final int WORKER_STATE_INIT = 0;
     public static final int WORKER_STATE_STARTED = 1;
     public static final int WORKER_STATE_SHUTDOWN = 2;
-    @SuppressWarnings({ "unused", "FieldMayBeFinal", "RedundantFieldInitialization" })
-    private volatile int workerState = WORKER_STATE_INIT; // 0 - init, 1 - started, 2 - shut down
+    @SuppressWarnings({ "unused", "FieldMayBeFinal" })
+    private volatile int workerState; // 0 - init, 1 - started, 2 - shut down
 
     private final long tickDuration;
     private final HashedWheelBucket[] wheel;