Thanks for the PR. There are several modules that seems to related to the dlg_flag:
* nat_traversal * call_control * cnxx * acc * qos * sst * pua_dialoginfo * mediaproxy * different IMS modules (ims_dialog will be not changed in this PR)
Some of the modules are using it only to check if there is a dialog module available. So this is probably not critical. But it needs to be investigated and probably changed. Some of the modules are just documenting it.