rmon counter read is less than ergonomic

The swadm command to read the rmon counters can return varying levels of detail. One specifies that level with a -l option. There is nothing to indicate what legal -l values might be or what they might mean. If we want to keep the same "level of detail" model, we should specify it with multiple -v options, which is a fairly standard idiom. We could also just have a single -v which distinguishes between minimal and maximal detail.

Start at the swadm rmon counter command and inspect how the -l option is parsed and how its help text describes the available detail levels. Determine whether the project should adopt repeated -v options or a single -v switch; done means the chosen interface has clear, documented semantics and the command's behavior matches them.