[fallback] Avoid duplicate old BootOrder

set_boot_order() already copies the old BootOrder to the variable,
bootorder. Besides, we can adjust BootOrder when adding the newly
generated boot option. So, we don't have to copy the old one again
in update_boot_order(). This avoid the duplicate entries in BootOrder.

Signed-off-by: Gary Ching-Pang Lin <glin@suse.com>
[fallback] Fix the data size for boot option comparison

Signed-off-by: Gary Ching-Pang Lin <glin@suse.com>
[fallback] Try to boot the first boot option anyway

Some UEFI implementations never care the boot options, so the
restored boot options could be just ignored and this results in
endless reboot.
To avoid this situation, this commit makes fallback.efi to
load the first matched boot option even if there is not boot
option to be restored.

Signed-off-by: Gary Ching-Pang Lin <glin@suse.com>