The maximum size of the data portion an echo
packet supported by this RTT application. This is
the maximum value that can be specified by
(rttMonEchoAdminPktDataRequestSize + ARR Header)
or
(rttMonEchoAdminPktDataResponseSize + ARR Header)
in the rttMonCtrlAdminTable.
This object is undefined for conceptual RTT
control rows when the RttMonRttType object is set
to 'fileIO' or 'script'.