core: don't automatically probe ports of USB<->serial adapters

We should not automatically probe ports marked as coming from USB to serial
adapters, as we're not sure that a modem is behind the adapter. Still, let the
user request a manual scan and have these devices probed in that case.

https://bugzilla.gnome.org/show_bug.cgi?id=647556
https://bugzilla.gnome.org/show_bug.cgi?id=691076

src/main.c

@@ -78,9 +78,9 @@ name_acquired_cb (GDBusConnection *connection,
 {
     mm_dbg ("Service name '%s' was acquired", name);
 
-    /* Launch scan for devices */
+    /* Launch automatic scan for devices */
     g_assert (manager);
-    mm_manager_start (manager);
+    mm_manager_start (manager, FALSE);
 }
 
 static void