net: handle >=2GiB files with sendfile on Windows
net: handle >=2GiB files with sendfile on Windows

CL 187037 applied a fix to handle the case where
files larger than 2GiB were not being sendfile-d,
in one shot, rejecting any files whose size was
larger than the 2GiB.

This CL allows files that are larger than limit
by SendFile-ing in chunks of upto 2GiB per chunk.

The test has been excluded as testing with 3GB
requires creating a local file, flushing it
and then doing sendfile which takes a while
and could cause flakes on computers without capacity,
but the test can be retroactively accessed at:
https://go-review.googlesource.com/c/go/+/192518/8/src/net/sendfile_windows_test.go

Fixes #33193.

Change-Id: If57c25bc289aec82b748890ac1ac4f55798d6a5e
Reviewed-on: https://go-review.googlesource.com/c/go/+/192518
Run-TryBot: Emmanuel Odeke <277f8eaa8c7dfbc55c17bf5e30561c1a9c45c569@gmail.com>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Alex Brainman <54ba58c8441b5eff861de6b4e5ee46baf086b142@gmail.com>

akutz/go,CAFxX/go,cloudflare/go,golang/go,CAFxX/go,golang/go,CAFxX/go,golang/go,cloudflare/go,nawawi/go,akutz/go,nawawi/go,golang/go,cloudflare/go,akutz/go,nawawi/go,CAFxX/go,golang/go,nawawi/go,CAFxX/go,cloudflare/go,akutz/go,akutz/go,cloudflare/go,CAFxX/go,akutz/go,akutz/go,nawawi/go,golang/go,cloudflare/go,CAFxX/go,akutz/go,golang/go,nawawi/go,cloudflare/go,golang/go,CAFxX/go,cloudflare/go,nawawi/go,nawawi/go