message: pnet_sys: touch up sin6_scope_id use
  Needed for send_to() to work with link-local addresses.
  Note that on the receive side, sin6_scope_id already appears to be in
  host byte order.
diff: @@ -138,6 +138,7 @@ pub fn addr_to_sockaddr(addr: SocketAddr,
  (*storage).sin6_family = AF_INET6 as SockAddrFamily6;
  (*storage).sin6_port = htons(addr.port());
  (*storage).sin6_addr = inaddr;
  + (*storage).sin6_scope_id = sa.scope_id();
  mem::size_of::<SockAddrIn6>()
  }
  };
  @@ -175,7 +176,7 @@ pub fn sockaddr_to_addr(storage: &SockAddrStorage, len: usize) -> io::Result<Soc
  Ok(SocketAddr::V6(SocketAddrV6::new(ip,
  ntohs(storage.sin6_port),
  u32::from_be(storage.sin6_flowinfo),
  - u32::from_be(storage.sin6_scope_id))))
  + storage.sin6_scope_id)))
  }
  _ => Err(io::Error::new(io::ErrorKind::InvalidData, "expected IPv4 or IPv6 socket")),
  }
  