Asterisk fixes for call waiting and 3way call
The commit includes lot of fixes for call waiting and 3way call:
- Call waiting is enabled/disabled now per feature_set. Each line has the feature_set defined and each provider (pjsip endpoint) has line selected. From now on call waiting status can be defined in uci config and changed by feature code, as a result corresponding feature set / endpoint cw status will be changed.
- Rename some functions and variables which had missleading names.
- Add 5s beep timer indicating incoming call waiting
- Fix 20s timeout when there is already another call in progress
- Fix call waiting/3way call for dect
- Implement "exceed call cound" check for line/extension