leaudio: Store chosen configuration asap

With this patch we store chosen configuration just when it got chosen
and not when streaming has started. In this way we make sure, this is
a correct configuration.

Bug: 210101068
Bug: 150670922
Test: atest --host  bluetooth_le_audio_client_test bluetooth_le_audio_test
Tag: #feature
sponsor: jpawlowski@
Change-Id: Ia7ca46228242b161894189ca0ef459b394bfc6c0