Use unique_ptr for upnp_thread (boost::thread)

src/net.cpp

@@ -1534,22 +1534,20 @@ void ThreadMapPort()
 
 void MapPort(bool fUseUPnP)
 {
-    static boost::thread* upnp_thread = nullptr;
+    static std::unique_ptr<boost::thread> upnp_thread;
 
     if (fUseUPnP)
     {
         if (upnp_thread) {
             upnp_thread->interrupt();
             upnp_thread->join();
-            delete upnp_thread;
         }
-        upnp_thread = new boost::thread(boost::bind(&TraceThread<void (*)()>, "upnp", &ThreadMapPort));
+        upnp_thread.reset(new boost::thread(boost::bind(&TraceThread<void (*)()>, "upnp", &ThreadMapPort)));
     }
     else if (upnp_thread) {
         upnp_thread->interrupt();
         upnp_thread->join();
-        delete upnp_thread;
-        upnp_thread = nullptr;
+        upnp_thread.reset();
     }
 }