Pass to RRC the 5G-S-TMSI extracted from NAS Registration Accept

* NAS -> RRC: RRC receives an ITTI message with NAS 5GMM indication message
  containing the 5G-S-TMSI derived from NAS GUTI
* 5G-S-TMSI is stored in the RRC instance and to be later encoded in the RRCSetup

openair2/COMMON/as_message.h

@@ -404,6 +404,13 @@ typedef struct nas_detach_req_s {
   bool wait_release;
 } nas_detach_req_t;
 
+/**
+ * @brief 5GS mobility management information
+ * @ref   clause 9.11.3 of 3GPP TS 24.501
+ */
+typedef struct nas_5gmm_ind_s {
+  uint64_t fiveG_STMSI;
+} nas_5gmm_ind_t;
 /*
  * --------------------------------------------------------------------------
  *              NAS information transfer
@@ -578,6 +585,7 @@ typedef struct as_message_s {
     rab_establish_cnf_t rab_establish_cnf;
     rab_release_req_t rab_release_req;
     rab_release_ind_t rab_release_ind;
+    nas_5gmm_ind_t Nas5GMMInd;
   } __attribute__((__packed__)) msg;
 } as_message_t;