bluetooth: delay automatic switch to a2dp from hfp.

The application create record(audio input), a2dp can automatic switch to hfp. When the application select or switch other audio input, current record close, no record, then create record. In the meantime， hfp can automatic switch to a2dp, then a2dp can automatic switch to hfp, bluetooth profile switch too frequently, and easy to have a certain impact on the application. For this problem，we can delay automatic switch to a2dp from hfp.