Implementation-specific data reported by the DLSw partner in a
HALT_DL or HALT_DL_NOACK, to help specify how and why this
circuit was last disconnected. If the partner does not send
this data in these messages, or the DLSw implementation does
not report receiving it, a string of zero length is returned.
This object is present only if the implementation keeps circuit
table entries around for some period after circuit disconnect.