This attribute specifies the transmit clocking mode.
If itc (Independent Transmit Clock) is chosen, the physical ports
used by the IMA group may have different clocking sources.
If ctc (Common Transmit Clock) is chosen, it is recommended that
the physical ports used by the IMA group have the same clocking
source. However, if the physical ports have different clocking
sources, the operator should ensure that all the clocking sources
have the same rate.