le_audio: Update in_call context in InCall mode

When falling back from InCall mode, update the metadata contexts
(previously set during InCall) with metadata updates from the Audio
Framework to ensure correct source/sink metadata is used.

Bug: 385380583
Test: atest bluetooth_le_audio_client_test
Flag: EXEMPT, day-to-day bugfix
Change-Id: Iccb21c565b7bacce6bb4553f92b0f0acf1b5f793