Expose the SelectorProvider used by the NioEventLoop

Motivation:

If a user writes an own nio based transport which uses a special SelectorProvider it is useful to be able to get the SelectorProvider that is used by a NioEventLoop. This way this can be used when implement AbstractChannel.isCompatible(...) and check that the SelectorProvider is the correct one.

Modifications:

Expose the SelectorProvider.

Result:

Be able to get the SelectorProvider used by a NioEventLoop.

transport/src/main/java/io/netty/channel/nio/NioEventLoop.java

@@ -184,6 +184,13 @@ public final class NioEventLoop extends SingleThreadEventLoop {
         return selector;
     }
 
+    /**
+     * Returns the {@link SelectorProvider} used by this {@link NioEventLoop} to obtain the {@link Selector}.
+     */
+    public SelectorProvider selectorProvider() {
+        return provider;
+    }
+
     @Override
     protected Queue<Runnable> newTaskQueue() {
         // This event loop never calls takeTask()