build: Modifications to facilitate OpenWRT builds of C sshnpd

[cpswan]

Putting the pieces in palace for OpenWRT builds

- What I did

• source tarball now has Makefile PKG_SOURCE as it's root
• added a CMakeLists.txt to packages/c

- How I did it

Multiple iterations using cpswan/release_automation repo

- How to verify it

Build against cpswan-sshnpd-cmake branch in Atsign_OpenWRT_packages repo

- Description for the changelog

build: Modifications to facilitate OpenWRT builds of C sshnpd