Fixes that namespaced views now also appear in the extra actions (#8598)

* Fixes that namespaced views now also appear in the extra actions

Before this fix, namespaced views would not appear in the extra actions. With this fix they do.

* Flake fix

Author: gabn88

rest_framework/viewsets.py

@@ -198,6 +198,10 @@ def get_extra_action_url_map(self):
         for action in actions:
             try:
                 url_name = '%s-%s' % (self.basename, action.url_name)
+                namespace = self.request.resolver_match.namespace
+                if namespace:
+                    url_name = '%s:%s' % (namespace, url_name)
+
                 url = reverse(url_name, self.args, self.kwargs, request=self.request)
                 view = self.__class__(**action.kwargs)
                 action_urls[view.get_view_name()] = url