Figured it out. Use the following code:

        req.setHeader('Content-Type', 'application/json');
        Http http = new Http();
        HTTPResponse res;
        try {
            res = http.send(req); 
        } catch (System.CalloutException e) {
            // add required action here, like calling the rest api again if need.
        }

Just put it in a try catch block and use the System.CalloutException