Update nr_nas_msg_sim.c. Enable the commented line 754 ( and disable 753) to work with the latest CN. 

In case of noS1-mode, we initialize the 'logicalChannelBearer_exist' array element for the pre-configured DRB0 in function 'nr_l2_init_ue()'.
That array is indexed with the LCID.
For DRB0, the LCID is 4.
Unfortunately, the code incorrectly used the array at index 0.
Therefore, the UE sent neither scheduling requests nor buffer status reports, what resulted in extremely poor UL throughput.

This commit enables UL traffic in do-ra mode by doing two changes:
- configure SDAP to send traffic to TUN interface instead of GTP by
  abusing enb_flag=0 (i.e., setting UE mode for gNB SDAP)
- manually enable RLC LCID in UE MAC, since nr_DRB_preconfiguration()
  statically enables one DRB bearer, without notifying MAC

NR_UE: slightly improve timing synchronization by minimizing the adjustment of the filtered peak position value

Start the new slot processing thread already before writing samples to the USRP.
This parallelizes slot processing and reading/writing samples from/to USRP.

t_reassembly timer as clp and also provision as per 38.821 7.2.2.1 when harq is enabled, scheduling_offset yet to be added

- with no-harq flag same harq ID can be reused for a new transmission.
- NO retransmission of unsuccessful transmissions with this flag.
- Each time NDI is flipped to ensure new data for transmission.
- UE will also not send any ACK for DL.

example for simulating 120ms one-way delay:
gNB: -P 7372800 --gnb_k2 480 --ul_sched_f 64
UE: -P 7372800 -A 14745600 --ue_slot_Rx_Tx 480 --ue_k2 480

- Add CL options for additional DURATION_RX_TO_TX and k2 value at UE, additional k2 at gNB
- Apply additional DURATION_RX_TO_TX at UE
- Apply the additional k2 at UE for scheduled msg3 by RAR and scheduled UL transmission by DCL. Re-compute the next Tx frame number
- Apply the additional k2 at gNB for scheduled msg3 and scheduled UL transmission. Re-compute the next Tx frame number
- Increase the RA window counter for reception of RAR
- Fix the data type for larger slot number in function get_samples_slot_timestamp
- Example for a one-way delay of 120ms: run gNB with "-P 7372800 --gnb_k2 480", run UE with "-P 7372800 -A 14745600 --ue_slot_Rx_Tx 480 --ue_k2 480"