Fix flaky test TestSrtpError, introduced in https://codereview.webrtc.org/1362913004.
Fix flaky test TestSrtpError, introduced in https://codereview.webrtc.org/1362913004.

BUG=webrtc:4690

Review URL: https://codereview.webrtc.org/1380103002

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#10137}

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