The type of the Spanning Tree Protocol which would be
running on this VLAN. This object is only instantiated
when the value of the corresponding instance of
vtpVlanEditType has a value of fddiNet(4) or trNet(5).
If 'ieee' is selected, the STP that runs will be IEEE.
If 'ibm' is selected, the STP that runs will be IBM.
If 'auto' is selected, the STP that runs will be
dependant on the values of vtpVlanEditBridgeType for all
children tokenRing/fddi type VLANs. This will result in
a 'hybrid' STP (see vtpVlanStpType).