library/ranap: enrich both t(s|r)_RANAP_DirectTransfer templates

Instead of having two similar variants of RANAP_DirectTransfer:

  - t(s|r)_RANAP_DirectTransfer, and
  - t(s|r)_RANAP_DirectTransferSAPI,

let's make the first one more flexible, and drop the last one.
This is achieved by introducing two supplementary functions:

  - f_gen_ts_dt_ies(), and
  - f_gen_tr_dt_ies,

which dynamically compose DirectTransfer.protocolIEs.

Change-Id: I7333d08c4d5a72159bfbd50fe8e7b1084cd61b9e
2 files changed