ltq-vdsl-app: make the dsl_control application stop cleanly

I am not calling dsl_cmd because I want to ignore the lock, quit
should also be send when someone else is accessing it. I saw that some
other call was stuck here and all following calls were stuck in the
dsl_cmd lock.

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>

SVN-Revision: 48943