Add methods to NetSocket for buffer handling

[erik777]

Using Vertx 4.2.7 currently.

Please add getWriteQueueSize. While writeQueueFull is useful, it would be helpful to see what the current write queue size used to calculate writeQueueFull is so we can offer multi-tiered escalation for back pressure handling instead of just full or not full. E.g., in a video stream pipe, can vary the quality based on different levels of backlog determined by the current write queue size.

Please add a public getWriteQueueMaxSize. There is currently a setWriteQueueMaxSize method with no corresponding getter. It would be useful to see what the current value is before changing it in pipeline handlers.