fix incoming call audio start time.

commit cec4abb2 fixing issue 6720482 had a flaw that
would insert commmands at the wrong position in the
audio policy service command thread queue causing other
commands to be delayed more than expected.

A change in track stop timing introduced by commit bfb1b832
made this issue visible when answering a call.

Bug: 10860012.
Change-Id: Iec769112f14e13d13b64628b808e43663e33771c