client-state: Config removal on ifdown and failure
ifstatus: Do not consider client-state in ifstatus

Rename status NOT_STARTED to UNCONFIGURED
client-state: Remove state
client-state: Set control flags to ifworkers and their children
xml: Fix functions adding numerical attrs
util: Add ni_var_array_remove() and ni_var_array_remove_at()
xml: Add xml_node_del_attr()
client-state: Turn <meta-data> into config node attrs