Add flag for call audio mode change.

Adding a flag for the new behavior which takes place when swapping between
a PSTN and VOIP call; this was a bug fix made to correct missing audio
mode transitions.

Bug: 289861657
Test: atest CallAudioManagerTest
Change-Id: I0feba38a3a529d139f251b995c0ddda40d89465b
4 files changed