This table extends the mplsTunnelTable to provide
per-tunnel packet performance information for the reverse
direction of a bidirectional tunnel. It can be seen as
supplementing the mplsTunnelPerfTable, which augments the
mplsTunnelTable.
For links that do not transport packets, these packet
counters cannot be maintained. For such links, attempts
to read the objects in this table will return
noSuchInstance.