Do the bytearray -> enum conversion here, so that everyone else than slavebase and slaveinterface (i.e. both the job and the slave) only see the enum.

QDataStream can be used to stream an int (the enum value) in and out, no need to use "strings" in the bytearray. Alternatively, QByteArray::number() can do the job as long as it's really just the one enum value that's needed here (and we know it will never need to be more...).