Thread affinity fix for scenario test SetMuted.
Thread affinity fix for scenario test SetMuted.

This is to satisfy a thread checker in AudioSendStream.

Bug: webrtc:9510
Change-Id: I5ba03562fcdc3e93d77707e41220b82b99581470
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/169343
Reviewed-by: Björn Terelius <efeae16329b3cb4ac5daf80d4bfda3344c027db3@webrtc.org>
Commit-Queue: Sebastian Jansson <c24d1bc144eb7c11e553f59153fa17dba85ca83e@webrtc.org>
Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#30648}

ShiftMediaProject/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,TimothyGu/libilbc,TimothyGu/libilbc