- Migrate libusb dependency back to libsane
  (virtually all useful backends for OpenWrt would need it anyway)
- Disabled new usb-record-replay feature (avoid libxml2 dep)
- Disabled new escl backend (network-only backend are not too useful
  for OpenWrt and it requires libcurl, libnetsnmp, libavahi and libxml2)
- Workaround sane-daemon/postinst installation on Imagebuild
- Enabled backends kvs40xx and mustek_usb2 (fixed upstream)
- Fix bigendian compilation
  (https://gitlab.com/sane-project/backends/-/merge_requests/329)
- Fix missing std::round() for uclibc
  (https://gitlab.com/sane-project/backends/issues/237)
- Fixes FS#2685: coldplug was running before usblp was loaded. Now
  it grants access do usblp when a device using it is plugged.

Signed-off-by: Luiz Angelo Daros de Luca <luizluca@gmail.com>

saned requires write access scanner USB bus for its process and
to usblp/bind in order to rebind multifunctional printers back
to usblp (for printing with p910nd).

A hotplug script monitor new USB devices for scanners. Scanners
are detected by searching /usr/share/sane/<vendor>-<backend>.usbid
for the device product_id.

The package saned creates user saned:scanners. Access is granted to
group scanners.

The default xinetd conf was updated to run as saned:scanner.

sane-daemon pkg now has a postinst trigger that runs udevtrigger for
granting perms where there are connected scanners during installation.

Existing hotplug scripts from hplip were removed. They were mostly
useless.

Signed-off-by: Luiz Angelo Daros de Luca <luizluca@gmail.com>