Gets the PKIFailureInfo bits the authority gave with a failure status, bit n of the BIT STRING as 1 << n
(0 badAlg, 2 badRequest, 5 badDataFormat, 14 timeNotAvailable, 15 unacceptedPolicy, 16 unacceptedExtension,
17 addInfoNotAvailable, 25 systemFailure), or null.
public int? FailureInfo { get; }
RFC 3161 §2.4.2, PKIFailureInfo.