Bluetooth: SDP: Fix the issue of not handling the next discovery req

The pending discovery request will not be handled in some cases.
The cases include,
- The received data length is not aligned with frame length
- The continuation status length is more than maximum value
- Total length of the response is less than the frame length
- Unknown operation code is received

There is also a case where the current discovery result was not
notified when processing the pending discovery request.
The cases include,
- Fail to send SDP request
- No tail room of received buffer to save the response data

Fix the issue by using the following steps,
- Notify the application that the discovery is done
- Process the pending discovery request

Signed-off-by: Lyle Zhu <lyle.zhu@nxp.com>