uxc: Add ubus bindings

[jasle]

Is it possible to add ubus bindings to uxc, so that other programs can list, create, start, stop, enable, disable and delete uxc using ubus?

[dangowrt]

As uxc itself is not a daemon running in background it cannot itself register with ubus to provide those methods. However, we could create something like rpcd-mod-uxc, and that should not be hard.