Set by the operator to indicate the PSN type on which this
VC will be carried. Based on this object, the relevant PSN
table entries are created in the in the PSN specific MIB
modules. For example, if mpls(1) is defined, the agent
create an entry in cpwVcMplsTable, which further define the
MPLS PSN configuration.
Note: the exact set of PSN types is yet to be worked
out by the WG.