ASTOBJ_INIT(user); // count = 1
ASTOBJ_CONTAINER_LINK(&conf->userl,user); // count = 2
ASTOBJ_CONTAINER_UNLINK(&conf->userl,user); // count = 1
ASTOBJ_UNREF(user, meetme_destroy_user);  // count = 1 (when =0 it fire the destroy)
at this point user= NULL