[low-power] enhance mCslFrameRequestAheadUs calculation for RCP
#101
| Job | Run time |
|---|---|
| 13m 58s | |
| 30m 23s | |
| 30m 47s | |
| 20m 6s | |
| 8m 51s | |
| 24m 27s | |
| 30m 49s | |
| 30m 8s | |
| 30m 35s | |
| 46s | |
| 3h 40m 50s |