[release-branch.go1.14] runtime: don't call wakeNetPoller during timerModifying
Reduce the length of time that other timer functions can see timerModifying.
In particular avoid system calls.
For #38023
Fixes #38051
Change-Id: I1b61229c668e6085d9ee6dca9488a90055386c36
Reviewed-on: https://go-review.googlesource.com/c/go/+/224902
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
(cherry picked from commit
355f53f0a0a5d79032068d4914d7aea3435084ec)
Reviewed-on: https://go-review.googlesource.com/c/go/+/225277