Test transfer of messages smaller than 64 byte

[papeg]

The smallest message size which can be configured in the example design is 64 bytes, which is the width of the FIFO. The aurora core itself sends messages in chunks of 32 bytes. This can be reached with setting the keep bits in a single transfer to half of the bytes. This should flush the datawidth converter and lead to a single transfer of the aurora core. With some small changes to the issue kernel, it could be verified, if this is really the case.