Client or server mark their pending objects with
the function g_isi_pending_set_owner().
When client or server get destroyed or reset the pending objects are
removed with the function g_isi_remove_pending_by_owner(). As a client
or server always uses only a particular resource, all the pending
objects are conveniently stored into a single list.
This new modem API supercedes the old client and server APIs. It
properly queues resource subscriptions and version queries, as well as
caches reachability status for a given resource.
Also, this is a complete redesign of ISI message handling, adding
another layer of abstraction to multiplexing operations to a given
modem resource.