leaudio: Fix handling active context type

Remote side provides us list of available context types.
For each of them, we search for best available configuration, however it
might happen that we might not find a configuration.
With this patch, when metadata changes to the context type which we
don't know configuration for, we will not proceed with it.

Bug: 232898053
Test: atest bluetooth_le_audio_test bluetooth_le_audio_client_test
Change-Id: I551bc46e7b1ac2c75be8ca90b31648f19c7db33b