audiopolicy: fix for voice call to work on USB headset during concurrency

When an input stream is active on USB headset and if a voice call
is received, the proxy_open() for voice call fails and the screen freezes.
All active inputs must be closed before opening input stream for
voice call and also all new requests to open input stream must be
blocked.

Change-Id: I3fb0d482a77495ff6fe9fcdc8a1f8915ade52c9a
CRs-fixed: 876993