samsung: fix up disconnect

Two issues here, first we dont' need to chain up to the parent
because it's not doing anything we need (it's mainly for PPP-based
devices) and second we need to wait a bit for the disconnect command
to complete by specifying a callback, otherwise the command may get
discarded when the port is shut down afterward.

plugins/mm-modem-samsung-gsm.c

@@ -672,24 +672,33 @@ do_connect (MMModem *modem,
     Samsung_call_control (MM_MODEM_SAMSUNG_GSM (info->modem), FALSE, old_context_clear_done, info);
 }
 
+static void
+disconnect_ipdpact_done (MMAtSerialPort *port,
+                         GString *response,
+                         GError *error,
+                         gpointer user_data)
+{
+    mm_callback_info_schedule ((MMCallbackInfo *) user_data);
+}
+
 static void
 do_disconnect (MMGenericGsm *gsm,
                gint cid,
                MMModemFn callback,
                gpointer user_data)
 {
+    MMCallbackInfo *info;
     MMAtSerialPort *primary;
     char *command;
 
+    info = mm_callback_info_new (MM_MODEM (gsm), callback, user_data);
+
     primary = mm_generic_gsm_get_at_port (gsm, MM_PORT_TYPE_PRIMARY);
     g_assert (primary);
 
     command = g_strdup_printf ("AT%%IPDPACT=%d,0", cid);
-
-    mm_at_serial_port_queue_command (primary, command, 3, NULL, NULL);
+    mm_at_serial_port_queue_command (primary, command, 3, disconnect_ipdpact_done, info);
     g_free (command);
-
-    MM_GENERIC_GSM_CLASS (mm_modem_samsung_gsm_parent_class)->do_disconnect (gsm, cid, callback, user_data);
 }
 
 static void