Netlink `SockProtocol`s

[sinkingpoint]

Currently the SockProtocol enum:

nix/src/sys/socket/mod.rs

Lines 81 to 95 in 4b6b14a

	#[derive(Clone, Copy, Debug, Eq, Hash, PartialEq)]
	pub enum SockProtocol {
	/// TCP protocol ([ip(7)](http://man7.org/linux/man-pages/man7/ip.7.html))
	Tcp = libc::IPPROTO_TCP,
	/// UDP protocol ([ip(7)](http://man7.org/linux/man-pages/man7/ip.7.html))
	Udp = libc::IPPROTO_UDP,
	/// Allows applications and other KEXTs to be notified when certain kernel events occur
	/// ([ref](https://developer.apple.com/library/content/documentation/Darwin/Conceptual/NKEConceptual/control/control.html))
	#[cfg(any(target_os = "ios", target_os = "macos"))]
	KextEvent = libc::SYSPROTO_EVENT,
	/// Allows applications to configure and control a KEXT
	/// ([ref](https://developer.apple.com/library/content/documentation/Darwin/Conceptual/NKEConceptual/control/control.html))
	#[cfg(any(target_os = "ios", target_os = "macos"))]
	KextControl = libc::SYSPROTO_CONTROL,
	}

is rather scarce. I'm looking into doing some Netlink work with Rust and the man page defines a number of protocols not currently supported by this enum (https://www.man7.org/linux/man-pages/man7/netlink.7.html). As far as I can tell this should just be a matter of adding them to it.