SAP: Handle disconnect indication message type properly

Usecase:
1) Connect DUT with Mecapp PC App supporting SAP
2) When SAP is connected, remove SIM card on DUT.

Expected Behaviour:
DUT should send disconnect indication to remote device

Observed behaviour:
DUT not sending disconnect indication to remote device

Root Cause:
DUT is not handling the message type for disconnection received
from RIL layer properly.

Fix:
Use correct message type for disconnect indication from RIL in
handleRilInd() API
(SapMessage.ID_DISCONNECT_IND -> SapMessage.ID_RIL_UNSOL_DISCONNECT_IND).

Test: Checked if disconnect indication is sent out when SIM card is removed.
Bug: 62937720
Change-Id: Ib63b7290d9f7c7af57ee25401d5bcfb7ba600b07