reset hfp_pending_cmd_ to handle retry logic

1. when a new session start, reset
2. when startStream failed, reset hfp_pending_cmd_ to allow retry
3. after suspendStream, reset hfp_pending_cmd_ to avoid stuck in pending suspend when SCO already disconnected

Bug: 367479598
Bug: 315234036
Flag: com::android::bluetooth::flags::is_sco_managed_by_audio and HFP session type only enabled when flag is enabled
Test: atest HeadsetStateMachineTest
Change-Id: I21f7091cf8965aed19c02da61e6c91bbd9f85172