leaudio: Do not attach device to the stream if not needed

Attach to stream might be triggered when remote change
available context types. Remote might do it, while it is already
in configuration process and stack should make sure, to not proceed
with attaching of such a device.

Bug: 342468300
Flag: EXEMPT, regression test with unit test, new test added
Test: atest bluetooth_le_audio_client_test
Change-Id: Id51f6ea70184d566894255e5620fa96370ac20e9