Indicates which type of packets will be sent and
accepted on this circuit. The values set will be
saved, but the values used will be modified by
the settings of isisSysLevelType. Thus, if the
isisSysTpe is level2 and the isisCircLevelType
for a circuit is level1, the circuit will not send
or receive IS-IS packets. This object follows the
ReplaceOnlyWhileDisabled behavior.