Also, In addition to a new API TSFetchFlagSet to set the fetch flags,
also need to change the return type for TSFetchUrl() to return the FetchSM
context.
TSFetchSM
TSFetchUrl(const char *headers, int request_len, sockaddr const *ip, TSCont
contp, TSFetchWakeUpOptions callback_options,
Sorry, I just realized that TSFetchUrl() can be called directly without
calling TSFetchCreate(). So, to preserve backward compatibility and to be able
to set the fetch flags, I'm going to add a new `TSFetchFlagSet` API as below.
The API accepts a previously created FetchSM context and the flags
