This might be possible, but I don't think it addresses the issue that such an exploit could be turned on and off remotely. The only way to be sure would be to do such sniffing all the time.
Re:There is no WhatsApp 'backdoor'
by NoodleIncident on Friday January 13, 2017 @07:50PM
(#13396112)
Is an app like this enough for that purpose?
https://play.google.com/store/apps/details?id=com.googlecode...
Has anyone performed such an audit?