cam: better ioctl compatibility for cd

[imp]

Summary

Unlike xpt and pass driver, there's no test for ENOTTY in cdioctl to try
the compatbility ioctls. Add one.

However, this is a disk ioctl, not a cdev ioctl. To get around this, we
cast the struct disk * to a struct cdev * to pass through. We cast it
back in a simple wrapper function.

Sponsored by: Netflix

[imp]

more direct call