sane-backends: update to 1.0.29

sane-backends: update to 1.0.29

- 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>