hw/rdma: Replace QList by GQueue

hw/rdma: Replace QList by GQueue

RdmaProtectedQList provides a thread-safe queue of int64_t on top of a
QList.

rdma_protected_qlist_destroy() calls qlist_destroy_obj() directly.
qlist_destroy_obj() is actually for use by qobject_destroy() only.
The next commit will make that obvious.

The minimal fix would be calling qobject_unref() instead.  But QList
is actually a bad fit here.  It's designed for representing JSON
arrays.  We're better off with a GQueue here.  Replace.

Cc: Yuval Shaia <yuval.shaia.ml@gmail.com>
Cc: Marcel Apfelbaum <marcel.apfelbaum@gmail.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20201211171152.146877-8-armbru@redhat.com>