Previously, we would require a @self argument and the @call_id in
nm_act_request_cancel_secrets(), although the @call_id already has
a pointer to @self.
In principle that is not necessary, but it makes the API a bit
more robust as you need to care about the lifetime of the @req
as well.
However it is a bit inconvenient, because it requires that caller to
track both the activation request and the call-id.
Now, allow nm_act_request_get_secrets() to instruct the call-id to
take an additional reference to @self. Later on, we would allow to omit
the argument during cancelling. We only allow this, if the call-id
takes a reference to @self.
