Add ipv6 multicast hops support

[ETKNeil]

This PR focus on adding ipv6 multicast hops support: See: https://man7.org/linux/man-pages/man7/ipv6.7.html See: https://learn.microsoft.com/en-us/windows/win32/winsock/ipproto-ipv6-socket-options

This is the same as multicast_ttl but for ipv6, it's also missing in Rust std

[ETKNeil]

the current checks failing are because https://docs.rs/libc/0.2.133/libc/fn.makedev.html removed the unsafe (see https://docs.rs/libc/0.2.132/libc/fn.makedev.html )

[sunfishcode]

The makedev fix has now landed on main; can you rebase this?

[ETKNeil]

The makedev fix has now landed on main; can you rebase this?

I rebased that branch onto your main

[sunfishcode]

Thanks!