reworking of MAC functions to schedule SSBs, including VRB map occupation and get_type0_PDCCH_CSS_config_parameters

- sorted out according to recurring logic that wants function
  prototypes in separate files from data struct and constants
  definitions, variables in separate .c files with inclusion
  of "extern" header files
- moved function prototypes to resective header files
- moved data structures and constants to respective header files
- merged unnecessary mac.h file into mac_defs.h @ MAC UE
- moved const variables suchs as tables to respective .c files
- moved extern references to respective extern.h files

This commit contains work done by Eurecom and by Benetel.

- Make required adaptations in RLC and default DRB configuration

- RA resource selection and transmission
- MAC header structs for RA
- RA procedure msg1 fixes
- code cleanup

- Updated PRACH procedures and general code formatting
- gNB msg1 handling and RAR generation
- general bug fixing
- formatting
- missing headers
- RAR handling.

nr-ip-UL-nos1: Fix packet corruption issue appearing with larger packet sizes based on iperf testing for the uplink

nr-ip-UL-nos1: Integrate NR MAC PDU structures for the Uplink. Currently supporting only data SDUs, Control Elements to be added.

clean code