The number of switched DS0 channels of the line.
This variable counts the number of wanLineChannels on an enabled
line with the wanLineChannelUsage of ds0-switched-channel(3) and
with any following wanLineChannelState bs-clear-pending(8),
bs-dialing(9), bs-ringing(10),and bs-connected(11) for all the
entries in its wanLineChannelEntry table.