Cancel networkStream.ReadAscync() on socket shutdown

Issue from LinkedIn:

```
Dan,
Is there any way I could cancel ReadAsync on NetworkStream object.
We get some threads blocked and can't close TcpClient underlying tcp connection. The reason i am asking as ReadAsync is overloaded method.
ReadAsync(Byte[], Int32, Int32, CancellationToken)
Any help will be greatly appreciated.
Best regards,
Rus
```