QLocalSocket: remove double buffer on qlocalsocket_unix

QLocalSocket: remove double buffer on qlocalsocket_unix

The QLocalSocket is using a QLocalUnixSocket which is a QTcpSocket
that has buffering enabled. Because QLocalSocket is a QIODevice it
also has its own read buffer. By opening the QIODevice Unbuffered
we only use the buffer in the QLocalUnixSocket.

Change-Id: I4b9091522f73b0831b20efb4a2a00c2603fc748b
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Richard J. Moore <rich@kde.org>
Reviewed-by: Lars Knoll <lars.knoll@nokia.com>
Reviewed-by: Shane Kearns <shane.kearns@accenture.com>