Eclipse ThreadX support

[beriberikix]

Microsoft recently donated ThreadX to Eclipse and it became released under a permissive open source license. Previously while closed source, ThreadX had a native CoAP implementation. However, in the transition it was removed. Adding ThreadX support could open up libcoap to additional users due to its usage in mission and safety critical applications.

I filed a similar request on the project.

[obgm]

Thanks for bringing this to our attention. I will check with volunteers if that is something to work on.