RFSIM UL errors

The CI results show PUSCH errors even in perfect channel conditions in some tests. After some investigation these seem to originate mostly from the mixed slots and for high MCS, e.g. 28. It can be reproduced even in phy-test mode with the following command

./nr-softmodem -O ../../../ci-scripts/conf_files/gnb.band78.106prb.rfsim.phytest-dora.conf --rfsim --phy-test --rfsimulator.serveraddr server -U 128 -t 28 -T 5

Where -T sets the number of RBs allocated to ULSCH. If this is changed to 10, the errors disappear. Even when using 5 not all the instances fail so it is really difficult to understand the underlying issue.