Changes

bts: f_verify_ramp_up(): fix RxLev / dBm mixup

Comparing RxLev and dBm values is comparing apples to oranges.  It's
just a lucky coincidence that fake_trx is using RF path loss value of
110 dB, which is also the offset between RxLev and dBm.

* Add `mp_rf_path_loss` matching the default value (110 dB) in fake_trx.
* Add `f_bts_max_rx_level_dbm()` calculating the expected Rx power level.
* Apply `rxlev2dbm()` on `l1_dl.dl_info.rx_level` whenever needed.
* Clarify the units in verdict / logging messages.

Change-Id: I818d18d6e0711247b73ee1f336133e2ed3f6e2cb
Related: OS#6939