"execute a command" ioctl that takes a dictionary as an argument
(specifying the command and arguments) and returns a dictionary
with the results (error code, optional error message, optional
result data).
- Define and implement a "get-properties" command for DRVCTLCOMMAND
that returns the properties dictionary of the specified device.
- Add a -p flag to drvctl(8) to fetch and display the properties of
the specified device.
This is a great example of how to use prop_dictionary_sendrecv_ioctl().
