res_smdi.c: Made use defaults if the smdi.conf file does not exist.

This module is an optional dependency of a couple of other modules.  If it
declines to load, it then forces other modules that can optionally use
this module to also decline.

* Made use the default configuration if the config file does not exist and
simplified some of the logic.

Change-Id: Ib93191f1fe28c0dd9ebe3d84c7762b32f83c4eb9