ltq-adsl: align config more closely to VDSL variants

ltq-adsl: align config more closely to VDSL variants

This is a preparation for adding support for dsl_cpe_pipe.sh with a
similar set of commands compared to the VDSL variant.

The configuration is simplified by using the "--enable-model" option.
Other options are chosen to match the VDSL variant, while also making
sure that previously enabled options stay like that. However, ReTx
options stay disabled, because of incompatibility with the ubus code.

Signed-off-by: Jan Hoffmann <jan@3e8.eu>
Link: https://patchwork.ozlabs.org/project/openwrt/patch/20241019174041.1281093-2-jan@3e8.eu/
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>