Additional index provided to distinguish between multiple tunnels to
same destination having same characteristics.
There could be multiple tunnels for the type 'sdp'. In such cases the
vRtrTunnelID will hold the SDP Id.
There could be multiple tunnels for the type 'ldp'. In such cases the
vRtrTunnelID will hold the LSPId of the LSP in use.
For other vRtrTunnelType values this field will always be 0 as only a
single tunnel is established using other tunnel types.