rrc: disable MAC bearers when RNTI gets updated

When the RRC handles the C-RNTI CE to update the RNTI, all the bearers
associated with the new RNTI (that will no longer be used) need to be disabled.
This commit implements this.

Signed-off-by: Carlo Galiotto <carlo@srs.io>

srsenb/hdr/stack/rrc/rrc_nr.h

@@ -122,6 +122,7 @@ public:
     // setters
 
     int pack_rrc_reconfiguration();
+    int deactivate_bearers();
 
   private:
     rrc_nr*  parent = nullptr;

srsenb/src/stack/rrc/rrc_nr.cc

@@ -189,6 +189,8 @@ int rrc_nr::update_user(uint16_t new_rnti, uint16_t old_rnti)
   // Remove new_rnti
   auto new_ue_it = users.find(new_rnti);
   if (new_ue_it != users.end()) {
+    // There is no need to check the return code, as this function should always return SUCCESS
+    new_ue_it->second->deactivate_bearers();
     task_sched.defer_task([this, new_rnti]() { rem_user(new_rnti); });
   }
 
@@ -1496,4 +1498,26 @@ int rrc_nr::ue::add_drb()
   return SRSRAN_SUCCESS;
 }
 
+/**
+ * @brief Deactivate all Bearers (MAC logical channel) for this specific RNTI
+ *
+ * The function iterates over the bearers or MAC logical channels and deactivates them by setting each of them to IDLE
+ *
+ * @return int SRSRAN_SUCCESS on success (only fails if the called sub-functions assert)
+ */
+int rrc_nr::ue::deactivate_bearers()
+{
+  // Iterate over the bearers (MAC LC CH) and set each of them to IDLE
+  for (auto& ue_bearer : uecfg.ue_bearers) {
+    ue_bearer.direction = mac_lc_ch_cfg_t::IDLE;
+  }
+
+  // No need to check the returned value, as the function will return SRSRAN_SUCCESS
+  parent->mac->ue_cfg(rnti, uecfg);
+
+  // Technically, the only way this function fails is if parent->mac->ue_cfg(rnti, uecfg) asserts
+  // Should we still return SRSRAN_SUCCESS or can we make it void?
+  return SRSRAN_SUCCESS;
+}
+
 } // namespace srsenb