Several other changes in this commit include:
- Setting the number of PDUS in the ul_config
  to be zero when we will it (inside of the
  get_ul_config() function.)
- We reset the nprach flag to 0 for each slot.
- We return out of the prach scheduler if
  mac->ul_config == NULL
- Added error checking for array indexing
- Created a dummy scheduler response function.
- Allocated ul_config_req initially