leaudio: Fix group set active race

When group is set active by Java and when this message goes down while
devices are being disconnected GroupSetActive function should return immediately.

Bug: 335290741
Test: atest bluetooth_le_audio_client_test
Flag: trivial fix, new unit test added.
Change-Id: Ie62dda6afb98a8044b58f58d4020babdc8f16a90