Struct packet_mreq requires repr(C) in rustc versions >= 1.67

[jahofmann]

With recent rustc versions the memory layout of packet_mreq pnet_datalink/src/bindings/linux.rs:32 has changed.

Rustc 1.67.0 is the first failing version for me and the problem could be related to rust-lang/rust#102750.

This leads to an error in pnet_datalink/src/linux.rs:124 as setsockopt receives the differently aligned struct and fails with "os error 19". In my case the IOCTL received 0 as the (invalid) device index.

Adding #[repr(C)] fixes the issue.

// man 7 packet
#[repr(C)]
pub struct packet_mreq {
    pub mr_ifindex: libc::c_int,
    pub mr_type: libc::c_ushort,
    pub mr_alen: libc::c_ushort,
    pub mr_address: [libc::c_uchar; 8],
}

[mrmonday]

This should be fixed in v0.32.0.