Update default commit and add rnnoise flag
Update DEFAULT_COMMIT to d8fdef7 so the recipe pulls the newer upstream revision by default, when the LATEST_REVISIONS environment variable is not set. This ensures the latest fixes and improvements from upstream are used when LATEST_REVISIONS is disabled or LINPHONE_SDK_REV is not set.
Add PACKAGECONFIG[rnnoise] to expose RNNoise support toggle. This allows building with or without RNNoise.