HSP: Keep sending RING message

Two PTS Test failed:
- HSP/AG/IAC/BV-01-I
- HSP/AG/ACR/BV-02-I

Reason:
AG didn't send the "RING" unsolicited result code to HS(PTS),
then HS can't send the "AT+CKPD=200" command to received the call.
After a while, the "FATAL ERROR (MTC): Call establishment timed out"
triggered by PTS.

Solution:
Keep sending RING message for HSP.

Bug: 77507028
Change-Id: If1288a5f7b1b7da8ecba34ed90a85a0af8a91e9a