audio policy: fix attributes for strategy "rerouting"

Strategy rerouting is used for audio injection to a recorder
dynamic audio policy mix. As such, the correponding audio attributes
must contain usage AUDIO_USAGE_VIRTUAL_SOURCE.

Test: gts-tradefed run gts --skip-device-info -m GtsGmscoreHostTestCases -t 'com.google.android.gts.audioservice.AudioServiceHostTest#testInjectForRecord'
Change-Id: Id175b9583faf8910aef7b2988ac5019d0cbbcb53