net: skip TestModeSocket on older Windows versions
CL 561937 taught os.Stat about IO_REPARSE_TAG_AF_UNIX and added a
test for it, TestModeSocket. This test fails on Windows older than
10.0.17063, in which AF_UNIX support was added. Skip the test on those
versions.
Some CI builders use Windows 10.0.14393, so CL 561937 broke them,
e.g. https://build.golang.org/log/
5ea4f6422779f32eccfef3a25df54283ddd4e65e.
Change-Id: I6c21a78a1454d2d88321478288c0da1b8a93e590
Reviewed-on: https://go-review.googlesource.com/c/go/+/563256
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Reviewed-by: Bryan Mills <bcmills@google.com>