The value of tmnxOtuIfPmTtiExpMode specifies the type of expected
Trail Trace Identifier (TTI) for the Path Monitoring (PM) in
the OTU overhead.
Specifying a tmnxOtuIfPmTtiExpMode value of 'auto (0)' along with
tmnxOtuIfPmTtiExp set with a single octet of '0xFF' will revert the
PM-TTI to the default which is 'all zeros' in tmnxOtuIfPmTtiExp.