Merge branch 'NR_RRC_harq_hacks' of https://gitlab.eurecom.fr/oai/openairinterface5g into NR_RRC_harq_hacks

Merge branch 'NR_RRC_harq_hacks' of https://gitlab.eurecom.fr/oai/openairinterface5g into NR_RRC_harq_hacks

  - The number of nb_dmrs_re at gNB side was set to 6, but here it is assumed
    that there will be no data allocation in OFDM symbols that carry DMRS
  - nb_dmrs_re that is being given as an input to the TBS calculation,
    should be multiplied by the number of DMRS symbols in order to get the total
    number of DMRS REs per RB
  - In the calculation of G, only the number of DMRS per RB in 1 OFDM symbol should
    be given as an input, because inside the function of the G calculation, this
    number is being multiplied by the number of OFDM symbols that carry DMRS

  - By default this value is equal to 0 at gNB in case of ulsim, but
    has a value in case of RF simulator
  - The N_TA_offset was calculated but not used at UE side

reverted handling of transform_precoding variable in NR FAPI. Added correct handling of this in ulsim.c

- get preamble from rach_ConfigDedicated in contention free mode
- do preamble selection only in prach slot

ENDC S1-U gNB support: Separate some GTP functions between eNB and gNB. Downlink traffic from SGW arrives properly at gNB now after path switch