Fixup various issues related to callwaitng, codec and internal call.
Backport the following commit:
Fix some callwaiting/unhold issues: asterisk-chan-voicemngr@bd688f0c
- With Flash spec uk, the call waiting indication tone is not stopped after acceptance.
- In some un-hold scenarios, pjsip was sent indicate as un-hold-transfer only and did nothing if it is not a transfer, which makes the local chan unable to un-hold.
Fix regression of g729 and internal call: asterisk-chan-voicemngr@2f7fb961