BDI is generated at the trail termination source point of
a return path in response to a defect detected at the trail
termination sink point of an LSP in the forwarding direction.
The frequency of BDI can be set by user.
Only valid for egress configuration.
The default value is detect frequency and it is valid only when a
backward-LSP exists.
0: per-second;
1: same as detect frequency.