Bluetooth: HFP_HF: Notify in-band ring setting

Handle the unsolicited result code +BSIR issued by the AG to indicate
to the HF that the in-band ring tone setting has been locally changed.

Add a callback `inband_ring` to notify the in-band ring tone setting.

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