Fix logging if debug logfile is disabled
Fix logging if debug logfile is disabled

In my previous [PR](https://github.com/raiden-network/raiden/pull/2021) there
was a mistake due to conditionally setting the level if disable debug logfile is
given.

This is now fixed and I tested both with and without `--disable-debug-logfile`
and the desired behaviour is now there.

hackaugusto/raiden,hackaugusto/raiden