selectedPLMN-Identity IE in RRCSetupComplete is an Index (long) of the PLMN selected
by the UE from the plmn-IdentityInfoList (SIB1) (see 3GPP TS 38.331)
while
Selected PLMN Identity in NGAP INITIAL UE MESSAGE Indicates the selected PLMN
id for the non-3GPP access (PLMN Identity ID carrying MNC, MCC and MNC size,
9.2.5.1 3GPP TS 38.413)
The legacy code was setting Selected PLMN Identity in the latter to an ID
value as the former, however in NGAP the IE to be encoded is PLMN Identity 9.3.3.5
therefore:
* set plmn type plmn_id_t in ngap_nas_first_req_t
* check whether received selectedPLMN-Identity is within bounds
* select PLMN from gNB_RrcConfigurationReq by selectedPLMN-Identity ID
note: this commit is assuming that the plmn-IdentityInfoList in SIB1
is matching the PLMN list in gNB_RrcConfigurationReq
* in NGAP: store the PLMN in the NGAP UE context, no need to fetch the PLMN
in the NGAP instance since the UE context already tells what PLMN
was selected
Closes#801