mac_pcap_base: fix race detected with TSAN

lib/include/srsran/common/mac_pcap_base.h

@@ -95,7 +95,7 @@ protected:
 
   std::mutex                              mutex;
   srslog::basic_logger&                   logger;
-  bool                                    running = false;
+  std::atomic<bool>                       running = {false};
   static_blocking_queue<pcap_pdu_t, 1024> queue;
   uint16_t                                ue_id = 0;