CSHARP-2459: Not outputting port to '+srv' urls

Having an issue with turning a mongourl to as string then re-parsing it. There is validation on parsing that the port cant be defined with '+srv' but the ToString() outputs the port

Author: Ethan Celletti

src/MongoDB.Driver/MongoUrlBuilder.cs

@@ -753,7 +753,7 @@ public override string ToString()
                 foreach (MongoServerAddress server in _servers)
                 {
                     if (!firstServer) { url.Append(","); }
-                    if (server.Port == 27017)
+                    if (server.Port == 27017 || _scheme == ConnectionStringScheme.MongoDBPlusSrv)
                     {
                         url.Append(server.Host);
                     }