nr,gnb,sched: avoid that ConRes CE gets allocated multiple times for the same Msg4

srsgnb/src/stack/mac/sched_nr_ue.cc

@@ -163,9 +163,11 @@ void ue::mac_buffer_state(uint32_t ce_lcid, uint32_t nof_cmds)
 
 void ue::rlc_buffer_state(uint32_t lcid, uint32_t newtx, uint32_t retx)
 {
-  if (lcid == 0) {
+  if (lcid == 0 and buffers.get_dl_tx_total(0) == 0) {
     // In case of DL-CCCH, schedule ConRes CE
-    // Note: use push_front because ConRes CE has priority
+    // Note1: rlc_buffer_state may be called multiple times for the same CCCH. Thus, we need to confirm lcid=0 buffer
+    //        state is zero to avoid that multiple CEs being scheduled.
+    // Note2: use push_front because ConRes CE has priority
     buffers.pending_ces.push_front({srsran::mac_sch_subpdu_nr::CON_RES_ID, cfg().carriers[0].cc});
   }
   buffers.dl_buffer_state(lcid, newtx, retx);