Made websocket maxFramePayloadSize configurable from WebSocketServerProtocolHandler.

Motivation:

Currently there's no way to configure maxFramePayloadSize from
WebSocketServerProtocolHandler, which is the most used entry point of
WebSocket server.

Modifications:

Added another constructor for maxFramePayloadSize.

Result:

We can configure max frame size for websocket packet in
WebSocketServerProtocolHandler. It will also keep backward compatibility
with default max size: 65536. (65536 is hard-coded max size in previous
version of Netty)