This commit introduces a delay mechanism for the first MIB/SIB transmission
in the gNB scheduler to allow PRACH noise estimate to converge stabilize
before first PRACH preamble reception.
Key changes:
- Added the `num_scheduled_prach_rx` variable to gNB_MAC_INST to keep track
of total number scheduled of PRACH receptions. Using uint64_t type to avoid
overflow.
- Updated the `gNB_dlsch_ulsch_scheduler` function to conditionally schedule
MIB/SIB transmissions if `num_scheduled_prach_rx` is at least 100.
The value comes from OAIs implementation of PRACH noise estimate.