On platforms with BSD-like sockets, it is useful for applications to have
access to the underlying file descriptor so that they can use functions like
select() and poll().
Do not promise that the field will exist on other platforms such as
Windows (where the type and name of the field are technically wrong because
Windows socket handles are actually not file descriptors).
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
b11d61e095