netlink: the channel is required by its own name #1306

require("netlink") requires the C module netlink.channel (lib/netlink.lua:10) and exposes netlink.channel = channel.new beside rt, genl and nl80211, so a script that only reads routes cannot load netlink without luanetlink.ko, and every one that does pins it until its state closes. The channel also has two spellings, netlink.channel(name) and require("netlink.channel").new(name), and the LDoc renders a function and a type under one name.

Decided for v5.0 (DEC-08): the umbrella keeps the Lua classes only, as #623 settled for them, and the channel is built like every C binding, require("netlink.channel").new(name). examples/linkflap, examples/netfailover and tests/netlink follow.

Part of #1292.