Fixup various issues related to callwaitng, codec and internal calls.

Backport the following commits:  
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