* Set the #LinphoneProxyConfig to use for the call
*
* @param params the #LinphoneCallParams @notnil
* @param proxy_config The #LinphoneProxyConfig to use, or NULL if none has been selected. The #LinphoneCallParams keep a reference on it and remove the older if it exists. @maybenil
* The application doesn't own a reference to the returned #LinphoneCall object.
* Use linphone_call_ref() to safely keep the #LinphoneCall pointer valid within your application.
* If the proxy is not specified in parameters, the caller proxy will be automatically selected by finding what is the best to reach the destination of the call.
* @param core #LinphoneCore object @notnil
* @param addr The destination of the call (sip address). @notnil