[#5862] Http2EventAdapter#onUnknownFrame(...) should throw Http2Exception

Motivation:

Http2EventAdapter implements the Http2FrameListener interface but implements the #onUnknownFrame(...) method without the interface's throws Http2Exception.

Modifications:

Add throws Http2Exception.

Result:

More correct method signature.

codec-http2/src/main/java/io/netty/handler/codec/http2/Http2EventAdapter.java

@@ -82,7 +82,7 @@ public class Http2EventAdapter implements Http2Connection.Listener, Http2FrameLi
 
     @Override
     public void onUnknownFrame(ChannelHandlerContext ctx, byte frameType, int streamId, Http2Flags flags,
-            ByteBuf payload) {
+            ByteBuf payload) throws Http2Exception {
     }
 
     @Override