Write DL ToA into circular buffer

In a future commit, we will look up the maximum ToA over the last
transmissions. Introduce a buffer in which we write the last
16 measurements.

openair1/PHY/INIT/nr_init_ue.c

@@ -157,6 +157,8 @@ void init_nr_prs_ue_vars(PHY_VARS_NR_UE *ue)
       for (int j=0; j<fp->nb_antennas_rx; j++) {
         prs_vars[idx]->prs_resource[k].prs_meas[j] = malloc16_clear(sizeof(prs_meas_t));
         AssertFatal((prs_vars[idx]->prs_resource[k].prs_meas[j]!=NULL), "%s: PRS measurements malloc failed for gNB_id %d, rx_ant %d\n", __FUNCTION__, idx, j);
+        prs_meas_t *m = prs_vars[idx]->prs_resource[k].prs_meas[j];
+        m->next_dl_toa = m->dl_toa;
       }
     }
   }