ltq-vdsl-vr11-app: exit more quickly if orderly shutdown fails

ltq-vdsl-vr11-app: exit more quickly if orderly shutdown fails

On exit, the app tries to do an orderly shutdown of the DSL connection
before it is stopped forcibly. Since the driver does 3 attempts with a
timeout of 2 seconds each, this might take about 6 seconds in the worst
case.

This is problematic on sysupgrade, because any process that doesn't exit
within 4 seconds is killed. This means that the DSL connection might not
be stopped at all before the actual system upgrade begins.

To avoid this, use the newly added option in the driver to not retry the
L3 request on failure.

Signed-off-by: Jan Hoffmann <jan@3e8.eu>
Link: https://patchwork.ozlabs.org/project/openwrt/patch/20250130102108.1606919-3-jan@3e8.eu/
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>