message: platform/redox: Support AF_UNIX in socket.
  To add support for UNIX sockets (AF_UNIX), of SOCK_STREAM type, the
  "chan:" scheme is used, which will be supportedby the ipcd running in
  userspace.
  Later commits add similar AF_UNIX support for the rest of the methods in
  impl PalSocket.
diff: @@ -292,7 +292,7 @@ impl PalSocket for Sys {
  }
  unsafe fn socket(domain: c_int, mut kind: c_int, protocol: c_int) -> c_int {
  - if domain != AF_INET {
  + if domain != AF_INET && domain != AF_UNIX {
  errno = syscall::EAFNOSUPPORT;
  return -1;
  }
  @@ -313,9 +313,10 @@ impl PalSocket for Sys {
  // The tcp: and udp: schemes allow using no path,
  // and later specifying one using `dup`.
  - match kind {
  - SOCK_STREAM => e(syscall::open("tcp:", flags)) as c_int,
  - SOCK_DGRAM => e(syscall::open("udp:", flags)) as c_int,
  + match (domain, kind) {
  + (AF_INET, SOCK_STREAM) => e(syscall::open("tcp:", flags)) as c_int,
  + (AF_INET, SOCK_DGRAM) => e(syscall::open("udp:", flags)) as c_int,
  + (AF_UNIX, SOCK_STREAM) => e(syscall::open("chan:", flags | O_CREAT)) as c_int,
  _ => {
  errno = syscall::EPROTONOSUPPORT;
  -1
  