log: new object logging support

So that we can provide the specific object id in every log associated
to a given object.

plugins/tests/test-keyfiles.c

@@ -65,7 +65,8 @@ test_foxconn_t77w968 (void)
 /************************************************************/
 
 void
-_mm_log (const char *loc,
+_mm_log (gpointer obj,
+         const char *loc,
          const char *func,
          guint32 level,
          const char *fmt,