Specifies the QoS shaping mode for this ATM port interface. 'frame'
indicates shaping is to be based on frames, not including cell
encapsulation and padding. 'cell' indicates shaping is to be based on
cells, with cell encapsulation and padding included.
'frame' mode can not be configured unless juniQosQosModePortFrameMode
for the ATM port interface is configured as 'lowLatency'.