Cap max data read by TcpConnection or NioConnection

Both NioConnection and TcpConnection read the length (4 bytes) first, then allocate a buffer and call InputStream.readFully().
If some random client (nc, curl, wget etc)connects accidentally, length might be huge and the memory allocation will fail with an OOME. This may even terminate the JVM, e.g. if -XX:+ExitOnOutOfMemoryError is set.
Solution: introduce an attribute which caps the max length, and throws an exception (closing the connection), avoiding reading the data. If 0, the length will not be capped.