[dart:io] Fix Unix domain socket headers for Fuchsia
[dart:io] Fix Unix domain socket headers for Fuchsia

Change-Id: I053b41e29184f5edb3d4f19573ead5124528f12c
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/140624
Reviewed-by: Zichang Guo <d26af3001798f91912fb1504666bca93c093d553@google.com>
Commit-Queue: Jason Simmons <345008440c885d4763d50f58e545b9839f60f79f@google.com>

dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk