usbconfig: implement -v option

[joerg]

Summary

Implement a -v option to usbconfig(8), as a shortcut for the most frequently needed commands dump_device_desc, dump_curr_config_desc, and show_ifdrv.
While here, implement a real -h option that has been promised by the man page.
Use <sysexits.h> to declare the utility return codes.

[• hselasky]

usr.sbin/usbconfig/usbconfig.c

275

Add a space before "[-v]".

614

use /* comments */ and not // comments

[joerg]

Well, with the additional space, one of the usage lines is now 79 characters ...

I thought // comments were now acceptable as they are in C since C99, a lot of /usr/src files have them, but you're right, style(9) doesn't mention them.

[• hselasky]

Don't forget to bump the manual page date again.

[joerg]

In D33586#758912, @hselasky wrote:

Don't forget to bump the manual page date again.

Hmm, it's still today's date. Does any automatic dependency strictly require a new date on each change?

[• hselasky]

Just set the date for tomorrow. There are some external scripts which look for date changes.

[joerg]

In D33586#758927, @hselasky wrote:

Just set the date for tomorrow. There are some external scripts which look for date changes.

OK, didn't knew that. I bumped it again, and pushed everything.
Thanks again for the speedy review!