res_smdi.c: Fix module ref counting and inverted test.

I think this module is so screwed up that it doesn't work anymore.  Even
with these attempts to fix things it still won't gracefully shut down.
The module refs will not go to zero to allow unloading the module.

* Fix module ref counting dealing with the SMDI interface object.  There
were several off-nominal paths that unbalanced the module ref count.  Also
the destructor freed the ao2 object itself which is bad.  Made the
smdi_read thread not hold its own ref to the SMDI interface object so when
all refs go away the destructor will stop the listener thread.

* Fixed the smdi_load() return code of 1 concerning the number of
listeners.  The test was inverted.

Change-Id: Ic288db51b58e395d6a2fc3847f77176c16988784