network: Move virObjectRef during AssignDef processing
    
    Move the virObjectRef in virNetworkObjAssignDefLocked to after
    the virHashAddEntry to make it "clearer" why the @ref is being
    incremented. Upon return from the ObjNew we will have 1 ref on
    the object already, adding it to the hash table requires the
    increment.
    
    Signed-off-by: John Ferlan <jferlan@redhat.com>