leaudio: Notify Offloader about disconnected CIS

Offloader might be not notified about disconnected CIS when ACL was
still there. This patch fixes this.

Bug: 331775328
Test: atest bluetooth_le_audio_test
Flag: Exempt, regression checked with unit tests.

Change-Id: Id7e08594e3c4b53d8222cc83bf35bd09017a1275