Improved backend transmission performance.

Reduced the memory overhead by removing the allocation
of a QDataStream QByteArray pair per packet.

Change-Id: I600fdbdd86b89e94ce2a025e95c9188e8b4a1c9c
Reviewed-by: Continuous Integration (KDAB) <build@kdab.com>
Reviewed-by: Brett Stottlemyer <bstottle@ford.com>