bts: fix TC_rsl_ms_pwr_dyn_ass_updown: simulate a good C/I value
Now that we populate the UL SACCH cache in advance, trxcon is sending ms-pwr-lvl 7 in the first UL SACCH block (as expected). This suddenly makes the testcase fail, because now the MS power loop is perfectly happy about the received input values and does not order any changes to the current MS power level anymore, contrary to our expectations.
Why? Short answer: because of C/I (curr 6, avg 6) being outside of the good range (thresh 13..17). The MS power loop intentionally avoids reducing Tx power because that would potentially degrade the link quality (C/I) even further. Solution: let's order fake_trx.py to simulate a C/I value that is within the thresholds.
This alone does not fix the testcase yet, another fix follows.
