Indicates the TDR test action to be executed on the interface
and whether the test is currently running or not.
'start' -- start the TDR test on the interface.
'clear' -- clear all the TDR test results on the interface.
After this action is executed on an interface,
the object value of ccdTdrIfResultValid for the
corresponding interface will be false(2).
'running' -- the TDR test is currently running on the
interface. This value is a read-only value
and can not be set on the interface.
'notRunning' -- the TDR test is currently not running
on the interface. This value is a read-only
value and can not be set on the interface.