LP#1336825 Fix log level on find_service warning

Sip::Configuration::find_service tries to log a warning when it does
not find a matching service defined for a given
address/port/protocol tuple.

This uses the correct LOG_WARNING log level, ensuring that the
desired message is logged.

Thanks to Jason Boyer for catching this!

Signed-off-by: Jeff Godin <jgodin@tadl.org>
Signed-off-by: Galen Charlton <gmc@esilibrary.com>