Variants of gupnp_service_action_get/set that use lists rather than
varargs. This is mainly done to allow PyGI to deal with service actions.
gobject-introspection do not (yet) support vararg and on top of that PyGI
maintainer refuses to handle reference type 'in' parameters correctly
because the only way to do that is 'inefficient'.

Co-author and reviewer: Zeeshan Ali (Khattak) <zeeshanak@gnome.org>