Develop nr merge

See merge request oai/openairinterface5g!588

Merge branch 'develop-nr-merge' of https://gitlab.eurecom.fr/oai/openairinterface5g into develop-nr-merge

Usrp ref locked

See merge request oai/openairinterface5g!657

Merge branch 'develop-nr-merge' of https://gitlab.eurecom.fr/oai/openairinterface5g into develop-nr-merge

For whatever reason, ru->frame_parms was NULL and the RRU crashed.
Let's allocated memory.

Also, don't do fp = ru->frame_parms in ru_thread, it seems that it
takes the value before allocation (so: NULL) and the code crashes
later on.

Maybe it's not the correct solution. To be refined at some point.

1. NR RU was using wrong config file descriptor. It should be the same as for the LTE RU and we should remove the NR RU config file descriptor (todo)
2. NR RU was calling feptx_prec from LTE RU procedures, which it should not. In the older versions this function didn't do anything anyway as there was a check on num_eNB, which is 0 for gNB. Now NR RU is not calling this function at all, but we have to write such a function for NR RU (todo)

Merge branch 'develop-nr-merge' of https://gitlab.eurecom.fr/oai/openairinterface5g into develop-nr-merge

Integration develop nr 2019w32

See merge request oai/openairinterface5g!656

Merge remote-tracking branch 'origin/update-to-2019-march-june-release' into integration_develop-nr_2019w32

ENDC for 5G NSA support: Basic implementation of x2ap_gNB_generate_ENDC_x2_setup_response() and x2ap_gNB_handle_ENDC_x2_setup_response()

ENDC for 5G NSA support (preparatory work): Basic implementation of x2ap_eNB_generate_ENDC_x2_setup_request() and x2ap_gNB_handle_ENDC_x2_setup_request()

Dual connectivity: Basic implementation of x2ap_eNB_handle_senb_addition_request and x2ap_eNB_generate_senb_addition_request_ack

- basic version of x2ap_eNB_generate_senb_addition_request with dumb values
- skeleton functions:
    - x2ap_eNB_handle_senb_addition_request
    - x2ap_eNB_handle_senb_addition_request_acknowledge
    - x2ap_eNB_handle_senb_addition_request_reject