leaudio: Improve inactivating group in error case

With this patch test code is improved to make sure that AF is stopped
from bluetooth side when device got inactivated due to error.

Also minor fix is added to clear the active group in the end of the
groupSetAndNotifyInactive.

Bug: 339801164
Test: atest bluetooth_le_audio_client_test
Flag: Exempt, trivial fix, regression tested with unit tests.
Change-Id: Idf1761615fba746013416d856e6d4c95abe048c2