Add ulsch decoding measurements, which are reported by nr_ulsim. Start ulsch_decoding_stats measurement before
nr_ulsch_decoding is called and stop it after collection of all decoder tasks from Tpool. In the context of nr_ulsim,
ULSCH_id is allways == 0, testing is performed per one TB, therefore measurement is started and stopped only once per trial.
Reported ulsch decoding statistics show the mean ulsch decoding time over x trials (specified by -n command line option of nr_ulsim).
This measurement does not provide valid information in case of nr-softmodem, when the loop is done over multiple ULSCH IDs -
start of the measurement is done multiple times and stops only once in this case.
For unitary physical simulators, ULSCH processing loop is executed only once
- the max number of PUSCH is set to 1. This ensures exactly one start and stop
of the ULSCH decoding time measurement per processed TB.

Note: ulsch decoding statistics reports average time of segmentation, rate matching, interleaving and decoding of the TB