le_audio: Don't QoS configure if streaming stopped

It may happen that while attaching the device t stream, the upper layer
stops the streaming. In such case, we shall ignore the ASE Codec
Configured notification and not start QoS Config operation.

Bug: 393098895
Flag: Exempt; regression covered by unit test added
Test: atest bluetooth_le_audio_test
Change-Id: I3bfe58d71140ecf764cef3980a2b4b0e8b89a731