Debugger: Allow transmissions of network packets in one go

We did call a flush() after every single packet, which was slowing down
things especially for the QDeclarativeDebugTrace service.

Change-Id: Idab074941a22364e154502eb12afa43b4dd33c22
Reviewed-by: Aurindam Jana <aurindam.jana@nokia.com>
Reviewed-by: Christiaan Janssen <christiaan.janssen@nokia.com>