introduce dedicated nr pdcp tick thread for F1 split

Currently, NR PDCP ticks are active only with monolithic gNB, triggered by the MAC scheduler in gNB_scheduler.c.
In F1 split mode, as there is no MAC, there’s no source to advance the NR PDCP timer via "nr_pdcp_wakeup_timer_thread()".
This commit introduces a dedicated thread for NR PDCP ticks in gNB-CU and CU-UP mode.
Without it, packet losses at the F1 uplink would cause indefinite buffering, as t-Reordering won't expire due to the lack of NR PDCP timer ticks.

executables/nr-cuup.c

@@ -168,7 +168,7 @@ int main(int argc, char **argv)
   AssertFatal(rc >= 0, "Create task for GTPV1U failed\n");
   rc = itti_create_task(TASK_CUUP_E1, E1AP_CUUP_task, NULL);
   AssertFatal(rc >= 0, "Create task for CUUP E1 failed\n");
-  nr_pdcp_layer_init(true);
+  nr_pdcp_layer_init();
   cu_init_f1_ue_data(); // for CU-UP/CP mapping: we use the same
   E1_t e1type = UPtype;
   MessageDef *msg = RCconfig_NR_CU_E1(&e1type);