Feature Request: Add support for `IP_HDRINCL` socket option

[NiiightmareXD]

Problem

I am currently working with raw sockets and need to set the IP_HDRINCL option to manually construct IP headers. Currently, rustix::net::sockopt does not appear to expose a wrapper for this option.

As a result, I have to fall back to unsafe code and libc to achieve this, which breaks the flow of using rustix for safe system calls.

Current Workaround

Currently, I have to implement it like this:

use rustix::fd::AsRawFd;

let one: i32 = 1;
unsafe {
    libc::setsockopt(
        fd.as_raw_fd(),
        libc::IPPROTO_IP,
        libc::IP_HDRINCL,
        std::ptr::from_ref::<i32>(&one).cast(),
        std::mem::size_of::<i32>() as u32,
    );
}

Proposed Solution

It would be great to add set_ip_hdrincl (and potentially get_ip_hdrincl) to rustix::net::sockopt.

Desired API:

// In rustix::net::sockopt

pub fn set_ip_hdrincl<Fd: AsFd>(fd: &Fd, value: bool) -> rustix::io::Result<()> {
    // ... implementation wrapping setsockopt with IPPROTO_IP / IP_HDRINCL
}

pub fn get_ip_hdrincl<Fd: AsFd>(fd: &Fd) -> rustix::io::Result<bool> {
    // ... implementation wrapping getsockopt
}

Context

This is standard functionality for raw socket programming (e.g., when building custom network tools) and seems to fit well within the scope of rustix's networking primitives.