### Description

I haven't found a way to skip CDR generation per call once [cdr_enable modparam](http://kamailio.org/docs/modules/devel/modules/acc.html#acc.p.cdr_enable) is enabled.

### Expected behavior

I have implemented via irontec/kamailio@38964a31d6c0158b7c9bb3abb4e9eb72aa8cd960 adding a new modparam with the dlg_var name that will prevent CDR generation for calls with that dlg_var set.

#### Actual observed behavior

Once CDR generation is enabled with [cdr_enable modparam](http://kamailio.org/docs/modules/devel/modules/acc.html#acc.p.cdr_enable) all calls generate CDR.

### Additional Information

I can make a PR adapting that patch and documenting new modparam, as long as there is no way of achieving it that I have missed and if you find it useful.

Thank you and regards,