The administratively assigned value for the contribution
of this port to the path cost of paths towards the root
of the corresponding Spanning Tree instance.
Writing a value of '0' assigns the automatically calculated
default Path Cost value to the port for this instance. If
the default Path Cost is being used, this object returns
'0' when read.
This complements the object etsysMstpPortOperPathCost,
which returns the operational value of the path cost.