net: TestWriteTimeoutFluctuation sometimes fails on 32-bit iOS builder

[mikioh]

See build dashboard.
http://build.golang.org/log/b02e6aaa2fe497fadf898192d5425e7201569703
http://build.golang.org/log/350de48b4c0e31390ac02f7a1af96c22401a5628
http://build.golang.org/log/58502b25b5c6dc158954ba111690223cb5bc078f
http://build.golang.org/log/2bb42bac80498052be38e335298d05b43d370f1a

No errors at the package API, looks like timeoutTransmitter goroutine is not scheduled well, not sure the reason but seems like it needs further investigation.

process continue
Process 580 resuming
--- FAIL: TestWriteTimeoutFluctuation (1.89s)

    timeout_test.go:706: Write took over 1s; expected 0.1s

FAIL

Process 580 exited with status = 1 (0x00000001) 
go_darwin_arm_exec: timeout running tests

[gopherbot]

CL https://golang.org/cl/9915 mentions this issue.

[bcmills]

Duplicate of #36108