HFP: Allow Audio Fwk to change HFP SCO volume when HFP profile is connected...

HFP: Allow Audio Fwk to change HFP SCO volume when HFP profile is connected and SCO is not connected

Align HFP's behavior with A2DP's. In A2DP, when music is not playing, user can change volume from phone. So HFP should do similarly, when HFP connected, and SCO is not connected, user can still change its volume from phone.

Bug: 348724965
Bug: 362313390
Change-Id: Ie17e51831a8911925001ee23c41336ef4267742c
Test: atest HeadsetStateMachine
Flag: com.android.bluetooth.flags.hfp_allow_volume_change_without_sco