An entry in this table is created for every MVPN tunnel
interface present in the device. The ifType for a MVPN
tunnel is 'tunnel' (131).
(A MVPN tunnel interface should have relevant generic
support in the IF-MIB and in the internet draft,
draft-thaler-inet-tunnel-mib. Only MVPN specific aspects
of such a tunnel interface are to be specified in this
table.)