Actually the instructions in that link don't put the 6100 in transparent bridge mode. They advise using a Bridge Mode of "routed bridge", and that doesn't work. One should choose a Bridge Mode of "bridge", as in this FAQ: »Verizon Online DSL FAQ
»How do I use a router with the Westell 6100?
to get a transparent bridge mode that works with a separate router.
But if the DSL link is disconnecting, the problem is a sync problem between the modem and the ISP's DSLAM, therefore not related to any router configuration.
When the DSL link is down, the DSL light on the 6100 should blink, (whether in bridge mode or not), to tell you that sync has been lost. The stats posted so far from that line don't look too bad but do seem to indicate an issue with the upstream, (low noise margin and incorrect sync rate). Watching for changes in those stats may help tell the tale.--
reboot, reset, reconfigure, then recycle.