channel.enable is currently ambiguous
For driver commands, enable refers to whether the channel acquires, but we probably want it to mean whether the channel gets measured.
The distinction is important for the trigger channel, which should be hardware enabled but for which we usually don't want to "measure". On the other hand, with 4+ channel oscilloscopes, there may be channels that we truly wish to switch off (because it allows more on-board memory for the other channels).
config.channel.enable currently refers to hardware enabling. At a future point, make config.channel.enable refer to enable measuring. Any measured channels or channels devoted to trigger will be hardware enabled.