audioservice: do not resume a2dp after sco reset if a2dp is disconnected

When BT headset disconnects during music playback with wired headset
connected, music will be routed to speaker and muted before new route
sets, but sound leakage on speaker may be observed because delayed A2DP
disconnection after SCO disconnection, causing unexpected music resume
on speaker for a short while.

Do not resume a2dp during SCO reset if A2DP device is disconnected.

CRs-Fixed: 2293689
Change-Id: Ic145dd16629565ebd8f5091e3a71f7e3ba8ddc06