Linux: Add support for the new get_capabilities ioctl

Linux: Add support for the new get_capabilities ioctl

* There were a few (new) usbdevfs capabilities which libusbx could not
  discover in any other way then checking the kernel version.
* However, this presents the following problems:
  1) It is just not very pretty
  2) Given the tendency of enterprise distros to backport stuff it is not
     reliable
  3) Some of these features turn out to not work with certain host controllers,
     making depending on them based on the kernel version not a good idea
* Therefore a new USBDEVFS_GET_CAPABILITIES ioctl has been added to the kernel
  to offer a better way to find out a device's capabilities (technically
  the capabilities of the host controller to which the device is attached,
  but that does not matter).