AudioPolicyManager: fix DTMF gain over BT SCO

Similarly to voice communication, DTMF usage gain must be maxed out
when playing over Bluetooth SCO to avoid the double attenuation.

Test: repro steps in bug
Flag: EXEMPT bug fix
Bug: 367200697
Change-Id: I24f28c7f36c13f94fb68b44a4a5a0ccebaad7158
1 file changed