switch-branch: prevent downgrades

Downgrades between versions is dangerous and can break router. It is not supported and all fixes and migration scripts are just one way, there is no way to revert changes done by them on downgrade. Thus doing downgrade can cause pretty much any component to become invalidly configured and thus broken.

Fixes: #741 (closed)

updater/switch-branch/files/switch-branch

@@ -120,6 +120,10 @@ fetch_target_version() (
 		"Turris Mox")
 			board="mox"
 			;;
+                *)
+                        echo "Unknown device model: '$OPENWRT_DEVICE_PRODUCT'" >&2
+                        return 2
+                ;;
 	esac
 	curl "https://repo.turris.cz/$1/$board/lists/turris-version"
 )