Content provider can't handle big byte data

[antreserv]

I've been using this test sftpserver with Paramiko.

If a file that is being "transferred" is bigger than the MAX_REQUEST_SIZE in Paramiko then the test sftpserver will not append the leftover data from subsequent packets.

I've narrowed down the line to this one https://github.com/ulope/pytest-sftpserver/blob/master/pytest_sftpserver/sftp/interface.py#L44 which just needs to account for the binary_data type in six.