Reopen output when routing changed for preferred mixer.

When output stream is open with preferred mixer attributes, it should
apply to the targeted device. In that case, when the routed device is
changed, close the output with preferred mixer attributes and reopen
with default configuration.

Bug: 239435816
Test: set preferred mixer attr, connect and disconnect BT while playing
      over USB device.
Test: atest audiopolicy_tests
Change-Id: I982c47d9786ae56314f7c8ba8c1361cd2c2e9f42