An NR-capable UE will transmit some NR measurements.
Once received, the whole process on nr-cell addition is started.
It will fail quickly.

Many things are still missing.

What is not handled properly with this commit:
- in x2ap_eNB_handle_sgNB_add_req we hardcode the gNB ID
- nr triggering is done if we receive a measurement but this measurement is
  not analyzed at all
- no timers (T_dc_overall, T_dc_prep) and as is the code fails and then the
  next triggering after UE reconnection will not work (x2 ID are not well
  handled here and there in the code)

Note also that the gNB part has not been looked at all for this commit.

This is work in progress...