ltq-vdsl-app: re-add lowlevel settings

ltq-vdsl-app: re-add lowlevel settings

Add back a slightly modified version of the lowlevel settings which
where removed with r46920.

In compare to the old lowlevel settings, the B43c tone is added to
tone_adsl_b and tone_adsl_bv.

If an unsupported tone value is used, the auto probing mode is used, in
compare to the fallback to tone_adsl_av and tone_vdsl_av with the old
lowlevel settings.

Signed-off-by: Mathias Kresin <openwrt@kresin.me>
git-svn-id: svn://svn.openwrt.org/openwrt/trunk@48054 3c298f89-4303-0410-b956-a3cf2f4a3e73