While the driver can be licensed under GPLv2 (all kernel drivers needs to be signed by Microsoft*, and VirtIO is a precedent¤ that you can do it), I'm not sure if the header should be licensed under GPLv2, mainly because it would stifle Wireguard adoption.
* In ordinary conditions. Test-sign mode does exist.
* In ordinary conditions. Test-sign mode does exist.
¤ ... for example, these Red Hat versions: https://www.catalog.update.microsoft.com/Search.aspx?q=Red%2...