Adding accept4(2) to NetBSD

[Thomasdezeeuw]

According to https://www.netbsd.org/changes/changes-8.0.html, NetBSD (x86_64-unknown-netbsd) has had the accept4(2) system call since February 2017. When the system call was added (#394, #546) it seems NetBSD 8.0 wasn't released yet (?).

I have two questions:

• Its it old/stable enough to add? Or is this crate targeting NetBSD 7.0?
• Can anyone with a NetBSD installation add the system call?

I would add it myself but I don't have a NetBSD installation so I would have no idea if I did it correctly, as NetBSD isn't run on the CI either (it seems).

Related: tokio-rs/mio#1213.

[krytarowski]

accept4(2) is not a system call, but a libc wrapper to paccept(2). Supporting <8.0 has little point here and it will go EOL in few months.