discover/device-handler: Restore autoboot setting on requery

When a device requery is triggered we cancel any default boot option on
the device. This also disables autoboot which we don't want; any boot
options found after the requery will not be able to autoboot.
To avoid this restore the existing autoboot setting after checking for
default options.

This prevents a particular corner case where a default boot option has
been selected for boot but one of its boot files has stalled or is
taking more time to download than the requery timeout and the requery
accidentally cancels autoboot preventing Petitboot from trying to boot
again.

Signed-off-by: Samuel Mendoza-Jonas <sam@mendozajonas.com>