filter-buffer: Add status_changed callback processing

filter-buffer: Add status_changed callback processing

While the status of filter-buffer changing from 'on' to 'off',
it need to release all the buffered packets, and delete the related
timer, while switch from 'off' to 'on', it need to resume the release
packets timer.

Here, we extract the process of setup timer into a new helper,
which will be used in the new status_changed callback.

Signed-off-by: zhanghailiang <zhang.zhanghailiang@huawei.com>
Cc: Jason Wang <jasowang@redhat.com>
Cc: Yang Hongyang <hongyang.yang@easystack.cn>
Signed-off-by: Jason Wang <jasowang@redhat.com>