syscall: on freebsd-386 only update written for certain errors
Testing on the freebsd-386 gomote seems to show that sendfile returns
a non-zero number of bytes written even when it returns EINVAL.
This confuses the caller. Change the Go code to only return non-zero
on success or EINTR or EAGAIN, which are the only cases where the
man page says that sendfile updates the number of bytes.
For #70763
Change-Id: Icc04e6286b5b29a2029237711d50fe4973234f0a
Reviewed-on: https://go-review.googlesource.com/c/go/+/635815 Reviewed-by: Ian Lance Taylor <iant@google.com>
Commit-Queue: Ian Lance Taylor <iant@google.com> Reviewed-by: Damien Neil <dneil@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>