sysupgrade: create 10_disable_services w/ fixed modified time

Every time "sysupgrade -b -" runs it would generate a new
(synthetic) "/etc/uci-defaults/10_disable_services" file with
the current time as the modified time.  This unfortunately
creates a non-deterministic tarball, so if you run a cron job
to save your state, you don't have a trivial way of seeing if
it changed or not without unpacking the archive, deleting this
file, and comparing the entire directory tree to the previous
backup.

fixes: 16145

Signed-off-by: Philip Prindeville <philipp@redfish-solutions.com>

package/base-files/files/sbin/sysupgrade

@@ -271,7 +271,7 @@ create_backup_archive() {
 				fi
 			done
 			disabled="$disabled\nexit 0"
-			tar_print_member "/etc/uci-defaults/10_disable_services" "$(echo -e $disabled)" || ret=1
+			tar_print_member "/etc/uci-defaults/10_disable_services" "$(echo -e $disabled)" "$(date -d "$(ls --full-time -ld /etc/rc.d | cut -c45-63)" "+%s")" || ret=1
 		fi
 
 		# Part of archive with installed packages info