The test has been flaky, probably due to EAGAIN, but let's find out
for sure.

Updates #25078

Change-Id: I5a5b14bfc52cb43f25f07ca7d207b61ae9d4f944
Reviewed-on: https://go-review.googlesource.com/109359
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Bryan C. Mills <bcmills@google.com>