The table containing indications of which VLANs are
preferred on which VLAN trunk ports. The preferred
VLANs on a trunk port have a lower Path Cost value
compared with the VLANs on the trunk not in the
preferred list. If the value of stpxSpanningTreeType
is neither pvstPlus(1) nor rapidPvstPlus(5), the
configuration in this table has no effect.