JFR events SocketReadEvent/SocketWriteEvent should contain exception information

Currently the JFR events SocketReadEvent and SocketWriteEvent are generated with a zero length transfer size when an exception occurs. Although a separate exception event is generated, it can be inconvenient to associate with the read/write that generated it. The SocketReadEvent and SocketWriteEvent can have an extra field with the exception message or null if the operation was sucessful.