This is going to be needed later, when some functions already
have the virNetworkObjList object already locked and need to
lookup a object to work on. As an example of such function is
virNetworkAssignDef(). The other use case might be in
virNetworkObjListForEach() callback.
Signed-off-by: NMichal Privoznik <mprivozn@redhat.com>