stack: fix issue where stack thread was exited before stop_impl was called

srsue/hdr/stack/mac/mac.h

@@ -171,6 +171,8 @@ private:
 
   mac_metrics_t metrics[SRSLTE_MAX_CARRIERS] = {};
 
+  bool initialized = false;
+
   /* Class to process MAC PDUs from DEMUX unit */
   class pdu_process : public thread {
   public:

srsue/src/stack/mac/mac.cc

@@ -88,14 +88,18 @@ bool mac::init(phy_interface_mac_lte* phy, rlc_interface_mac* rlc, rrc_interface
 
   reset();
 
+  initialized = true;
+
   return true;
 }
 
 void mac::stop()
 {
-  pdu_process_thread.stop();
-
-  run_tti(0); // make sure it's not locked after last TTI
+  if (initialized) {
+    pdu_process_thread.stop();
+    run_tti(0); // make sure it's not locked after last TTI
+    initialized = false;
+  }
 }
 
 void mac::start_pcap(srslte::mac_pcap* pcap_)

srsue/src/stack/ue_stack_lte.cc

@@ -130,14 +130,14 @@ void ue_stack_lte::stop()
 {
   if (running) {
     pending_tasks.push([this]() { stop_impl(); });
-    running = false;
-
     wait_thread_finish();
   }
 }
 
 void ue_stack_lte::stop_impl()
 {
+  running = false;
+
   usim->stop();
   nas.stop();
   rrc.stop();