Unrecognized Content-Security-Policy directive 'webrtc' in browser console

The webrtc directive is defined in the CSP spec, but is not yet implemented by all browsers. The message is only displayed in the browser console, and it does not send a violation report if you have configured a reporting option.
https://www.w3.org/TR/CSP3/#directive-webrtc

The module config form defaults to 'block' when enabled, but if the directive is not yet supported by a browser (or not present in the policy), then webrtc connections are allowed by the browser by default (webrtc 'allow' is explicit, but functionally the same as omitting the directive). Nothing you can do about that, but if you're not using webrtc and want browsers to block it when they add support, you can enable the directive with 'block' now.