lib,rlc_am_nr: add stop() method to TX entity

lib/include/srsran/rlc/rlc_am_nr.h

@@ -98,6 +98,7 @@ public:
 
   void reestablish() final;
   void stop() final;
+  void stop_no_lock();
 
   int  write_sdu(unique_byte_buffer_t sdu);
   void empty_queue() final;

lib/src/rlc/rlc_am_nr.cc

@@ -1167,7 +1167,33 @@ void rlc_am_nr_tx::empty_queue_no_lock()
     unique_byte_buffer_t buf = tx_sdu_queue.read();
   }
 }
-void rlc_am_nr_tx::stop() {}
+
+void rlc_am_nr_tx::stop()
+{
+  std::lock_guard<std::mutex> lock(mutex);
+  stop_no_lock();
+}
+
+void rlc_am_nr_tx::stop_no_lock()
+{
+  empty_queue_no_lock();
+
+  if (parent->timers != nullptr && poll_retransmit_timer.is_valid()) {
+    poll_retransmit_timer.stop();
+  }
+
+  st = {};
+
+  sdu_under_segmentation_sn = INVALID_RLC_SN;
+
+  // Drop all messages in TX window
+  tx_window->clear();
+
+  // Drop all messages in RETX queue
+  retx_queue->clear();
+
+  tx_enabled = false;
+}
 
 void rlc_am_nr_tx::timer_expired(uint32_t timeout_id)
 {