pcap: add dtor

this fixes issue if object is destroyed and PCAP is still open

lib/include/srslte/common/mac_pcap.h

@@ -30,7 +30,8 @@ namespace srslte {
 class mac_pcap
 {
 public:
-  mac_pcap() {enable_write=false; ue_id=0; pcap_file = NULL; };
+  mac_pcap();
+  ~mac_pcap();
   void enable(bool en);
   void open(const char *filename, uint32_t ue_id = 0);
   void close();

lib/src/common/mac_pcap.cc

@@ -26,6 +26,13 @@
 
 namespace srslte {
 
+mac_pcap::mac_pcap() : enable_write(false), ue_id(0), pcap_file(nullptr) {}
+
+mac_pcap::~mac_pcap()
+{
+  close();
+}
+
 void mac_pcap::enable(bool en)
 {
   enable_write = true; 
@@ -39,8 +46,11 @@ void mac_pcap::open(const char* filename, uint32_t ue_id)
 void mac_pcap::close()
 {
   enable_write = false;
-  fprintf(stdout, "Saving MAC PCAP file\n");
-  LTE_PCAP_Close(pcap_file);
+  if (pcap_file != nullptr) {
+    fprintf(stdout, "Saving MAC PCAP file\n");
+    LTE_PCAP_Close(pcap_file);
+    pcap_file = nullptr;
+  }
 }
 
 void mac_pcap::set_ue_id(uint16_t ue_id) {