Add an unstable `const_sockaddr_setters` feature Unstably add `const` to the `sockaddr_setters` methods. Included API: ```rust // core::net impl SocketAddr { pub const fn set_ip(&mut self, new_ip: IpAddr); pub const fn set_port(&mut self, new_port: u16); } impl SocketAddrV4 { pub const fn set_ip(&mut self, new_ip: Ipv4Addr); pub const fn set_port(&mut self, new_port: u16); } impl SocketAddrV6 { pub const fn set_ip(&mut self, new_ip: Ipv6Addr); pub const fn set_port(&mut self, new_port: u16); } ``` Tracking issue: <https://github.com/rust-lang/rust/issues/131714>