This appears to be strictly a packaging problem in our Ubuntu builds. On some branches shared library .so files aren't packaged into any .deb packages at all. On others they are packaged into a different .deb package than the tools that use them.

lnetctl is in the lustre-utils .deb package. Our shared libs used by our own tools should be in that same package, but they are not. When lustre-utils is installed on Ubuntu lnetctl won't run because the liblnetconfig.so it is linked with is not there.
I will push a small patch to fix this.