AudioService: increase audio mode timeout.

Increase audio mode timeout from 3 seconds to 6 seconds
to leave more time for VoIP apps to connect the call after
setting the audio mode.

Bug: 174714082
Test: repro steps in the bug
Change-Id: Ic1efc496931a5ab5fb9a28fc918dba1cf66a89df
Merged-In: Ic1efc496931a5ab5fb9a28fc918dba1cf66a89df