fix memory leak in dns unittest

ixwebsocket/IXDNSLookup.cpp

@@ -68,6 +68,11 @@ namespace ix
                            : resolveUnCancellable(errMsg, isCancellationRequested);
     }
 
+    void DNSLookup::release(struct addrinfo* addr)
+    {
+        freeaddrinfo(addr);
+    }
+
     struct addrinfo* DNSLookup::resolveUnCancellable(
         std::string& errMsg, const CancellationRequest& isCancellationRequested)
     {

ixwebsocket/IXDNSLookup.h

@@ -31,6 +31,8 @@ namespace ix
                                  const CancellationRequest& isCancellationRequested,
                                  bool cancellable = true);
 
+        void release(struct addrinfo* addr);
+
     private:
         struct addrinfo* resolveCancellable(std::string& errMsg,
                                             const CancellationRequest& isCancellationRequested);