src/new/netbsd/net/if_.rs: make if_msghdr self-tests succeed on ilp32 hosts:

This fixes the following errors from `cd libc-test; cargo test`:

    bad `if_msghdr` size: rust: 148 != c 152
    bad `if_msghdr` align: rust: 4 != c 8
and
    size of `struct if_msghdr` is 152 in C and 148 in Rust

as verified natively on NetBSD/i386 10.0 with rust 1.92.0.

Ref. https://nxr.netbsd.org/xref/src/sys/net/if.h#790 for the
original C definition of `struct if_msghdr`.

(backport <rust-lang#4902>)
(cherry picked from commit 86dbfd4)

Author: he32

src/new/netbsd/net/if_.rs

@@ -50,6 +50,7 @@ pub const IFF_LINK2: c_int = 0x4000; // per link layer defined bit
 pub const IFF_MULTICAST: c_int = 0x8000; // supports multicast
 
 s! {
+    #[repr(C, align(8))]
     pub struct if_msghdr {
         pub ifm_msglen: c_ushort,
         pub ifm_version: c_uchar,