Add exclusive_address and set_exclusive_address

[bhaskargurram-ai]

Adds Windows only Socket::exclusive_address and Socket::set_exclusive_address for the SO_EXCLUSIVEADDRUSE option, the opposite of SO_REUSEADDR, as suggested in #676: a socket bound without it can have its port taken over by another socket that sets SO_REUSEADDR, and there is currently no way to set the option through socket2 or std.

The methods live in the Windows only impl Socket block in src/sys/windows.rs behind the all feature, next to set_no_inherit and protocol, and mirror reuse_address/set_reuse_address. The getter uses the Bool helper so both the 1 byte and 4 byte replies Windows gives for boolean options are handled. The docs note that the option has to be set before bind.

let socket = Socket::new(Domain::IPV4, Type::STREAM, None)?;
socket.set_exclusive_address(true)?;
socket.bind(&"0.0.0.0:8080".parse::<SocketAddr>()?.into())?;

Adds a test!(exclusive_address, set_exclusive_address(true)) get/set test gated on all(feature = "all", windows). Checked with cargo check --target x86_64-pc-windows-msvc --features all --all-targets (also with windows-sys pinned to 0.60.2), cargo doc with -D warnings for that target, cargo test --features all, cargo fmt --check and cargo clippy --all-targets --features all -- -D warnings on Linux.

Closes #676

[Thomasdezeeuw]

Can you add that this is only true for Windows?

[bhaskargurram-ai]

Done in bf27653, the docs now say the SO_REUSEADDR takeover is Windows behaviour, not Unix. Thanks for the review!

[Thomasdezeeuw]

Thanks @bhaskargurram-ai