The value of tmnxOtuIfPsiTtiExpMode specifies the type of expected
Trail Trace Identifier (TTI) Payload Structure Identifier (PSI) in
the OTU overhead.
Specifying a tmnxOtuIfPsiTtiExpMode value of 'auto (0)' along with
tmnxOtuIfPsiTtiExp set with a single octet of '0xFF' will revert the
PSI-TTI to the default which is 'all zeros' in tmnxOtuIfPsiTtiExp.