Fix NetBSD build error due to UData type mismatched

[AaronChen0]

libc 0.2.178 changed the type of kevent.udata to brings it in line with other BSDs.

Without this pull request, netbsd build failed with the following error.

error[E0308]: mismatched types
   --> /home/runner/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/mio-1.1.0/src/sys/unix/selector/kqueue.rs:64:20
    |
 64 |             udata: $data as UData,
    |                    ^^^^^^^^^^^^^^ expected `*mut c_void`, found `isize`
...
137 |             let kevent = kevent!(fd, libc::EVFILT_WRITE, flags, token.0);
    |                          ----------------------------------------------- in this macro invocation
    |
    = note: expected raw pointer `*mut c_void`
                      found type `isize`
    = note: this error originates in the macro `kevent` (in Nightly builds, run with -Z macro-backtrace for more info)

Reference:
rust-lang/libc@63f4037
https://github.com/shadowsocks/shadowsocks-rust/actions/runs/19874531148/job/56958491608

[Darksonn]

Thanks.