Remove NR L2 simulator code from UE
This MR removes NR (SA and NSA) L2 simulator from the codebase. The code, at
least at the UE side, was done at a time where there was no clear L2/L1 split
leading to a complex implementation that never worked as expected. The L2
simulator has been broken and removed from testing for long time and, once it
needs to be revived, it would require a complete new implementation.
- Replaced ITTI message queues with notifiedFIFO for RRC to MAC communication in UE.
- Enables correct message delivery to multiple MAC instances running in parallel threads.
- Introduced `nr_mac_rrc_message_t` union for MAC-RRC messages.
- Updated all relevant message handling and initialization code to use notifiedFIFO.
Reduce race conditions through a itti queue, such that RRC-initiated MAC
memory modifications happen at the same time as MAC thread writes.
However, it doesn't resolve the problem of exact slot we should apply
the new cell configurtion.
Thomas Schlichter