managerd: Harmonize the default bootlimit to 3

On U-Boot platforms the default bootlimit is set in the bootloader itself with CONFIG_BOOTCOUNT_BOOTLIMIT=3 (see the apertis/imx6/0003-mx6sabrelite-enable-bootcount.patch and apertis/renesas/0003-renesas-enable-bootcount.patch patches), so let's default to three failed boots before rollback here to have a more consistent behavior across platforms.

This in particular affects the UEFI platforms (amd64).

debian/changelog

+apertis-update-manager (0.2020.31) apertis; urgency=medium
+
+  * managerd: Harmonize the default bootlimit to 3
+
+ -- Emanuele Aina <emanuele.aina@collabora.com>  Tue, 04 Jan 2022 16:00:05 +0000
+
 apertis-update-manager (0.2020.30) apertis; urgency=medium
 
   [ Gireesh Hiremath ]