[RTA/DPA BW tests]: Follow Moore!4975
Needs to go in with lhcb/Moore!4975 (merged)
In that MR we started doing GB/s -> MB/s in the per-line and per-stream comparisons, so follow that here.
Will break any comparison with a reference that is still in GB/s, so should be merged with the upstream MRs just before a nightly build so that no-one has time to try a MB/s - GB/s comparison.