fix(openthread-br): switch to unprivileged container

USB passthrough works unprivileged. Network operations (iptables,
interface creation) should work with nesting enabled.

ct/openthread-br.sh

@@ -13,7 +13,7 @@ var_ram="${var_ram:-2048}"
 var_disk="${var_disk:-4}"
 var_os="${var_os:-debian}"
 var_version="${var_version:-13}"
-var_unprivileged="${var_unprivileged:-0}"
+var_unprivileged="${var_unprivileged:-1}"
 
 header_info "$APP"
 variables