gNB: modify RLC configuration applied for SRB1 during RRCReestablishment

TS 38.331 clause 5.3.7.4 specifies to apply the configuration defined in 9.2.1 for SRB1 at UE side.
This implies that the gNB also has to apply sn_field_length = 12, but there are no implications on the other RLC parameters.

As wrong timer values break SRB1 e.g. for long RTT NTN scenarios, this commit switches to using the RLC timer values provided in the configuration file.
Currently we still set poll_pdu, poll_byte and max_retx_threshold to the values defined in 9.2.1, but this can be changed.

openair2/LAYER2/NR_MAC_gNB/mac_rrc_dl_handler.c

@@ -980,8 +980,15 @@ void dl_rrc_message_transfer(const f1ap_dl_rrc_message_t *dl_rrc)
     pthread_mutex_unlock(&mac->sched_lock);
     nr_rlc_remove_ue(dl_rrc->gNB_DU_ue_id);
     nr_rlc_update_id(*dl_rrc->old_gNB_DU_ue_id, dl_rrc->gNB_DU_ue_id);
-    /* 38.331 clause 5.3.7.4: apply the specified configuration defined in 9.2.1 for SRB1 */
-    nr_rlc_reconfigure_entity(dl_rrc->gNB_DU_ue_id, 1, NULL);
+    /* 38.331 clause 5.3.7.4: apply gNB RLC configuration for SRB1 to match the UE RLC configuration defined in 9.2.1 */
+    nr_rlc_configuration_t rlc_configuration = mac->rlc_config; // use configuration file values for timers t_poll_retransmit, t_reassembly and t_status_prohibit
+    rlc_configuration.srb.poll_pdu = -1;
+    rlc_configuration.srb.poll_byte = -1;
+    rlc_configuration.srb.max_retx_threshold = 8;
+    rlc_configuration.srb.sn_field_length = 12;
+    NR_RLC_Config_t *rlc_Config = nr_srb_config(&rlc_configuration);
+    nr_rlc_reconfigure_entity(dl_rrc->gNB_DU_ue_id, 1, rlc_Config);
+    ASN_STRUCT_FREE(asn_DEF_NR_RLC_Config, rlc_Config);
     instance_t f1inst = get_f1_gtp_instance();
     if (f1inst >= 0) // we actually use F1-U
       gtpv1u_update_ue_id(f1inst, *dl_rrc->old_gNB_DU_ue_id, dl_rrc->gNB_DU_ue_id);