ltq-vdsl-vr11-app: perform orderly shutdown on exit

ltq-vdsl-vr11-app: perform orderly shutdown on exit

Try to do a clean disconnection via L3 request before the connection is
stopped.

Because this might take up to 6 seconds (the driver does 3 attempts with
a timeout of 2 seconds each), a termination timeout needs to be defined
in the init script.

Signed-off-by: Jan Hoffmann <jan@3e8.eu>