leaudio: Do not trigger QoS config if device is not ready

Remote device might sent CONFIGURED state just after reconnection, but
from the stack point of view device is no yet ready to be attached to
the stream e.g. MTU exchange is not completed.

Stack will attach device to the stream once it is ready.

Bug: 302279664
Test: atest bluetooth_le_audio_test
Tag: #feature
Change-Id: Ic778093cfc531e061c15bff2c65df30ea7901933