Factor common RAW AF_PACKET socket pattern

[sneaky-potato]

Move recurring raw socket receive and send pattern in a common place.

Fixes #358

[lneto]

I would use the very same approach we use on unix.lua; we can leverage the new() function we have there to better modularize our code here..

could you also apply this new lib on the examples that should use it on this PR?

[lneto]

btw, please use --fixup on your commits or squash it.. let's keep our history as clean as possible

[lneto]

Suggested change

	local function new(method)
	raw[method] = function (proto, ifindex)
	local proto = proto or ETH_P_ALL
	local ifindex = ifindex or 0
	local s = socket.new(af.PACKET, sock.RAW, proto)
	s:bind(string.pack(">H", proto), ifindex)
	return s
	end
	end
	---
	-- Creates and binds a raw packet socket for receiving and sending frames.
	-- @param proto (number) EtherType (defaults to ETH_P_ALL).
	-- @param ifindex (number) Interface index.
	-- @return A new raw packet socket bound for RX.
	-- @raise Error if socket.new() or socket.bind() fail.
	-- @see socket.new
	-- @see socket.bind
	new("bind")
	---
	-- Creates and binds a raw packet socket for receiving and sending frames.
	-- @param proto (number) EtherType (defaults to ETH_P_ALL).
	-- @param ifindex (number) Interface index.
	-- @return A new raw packet socket bound for RX.
	-- @raise Error if socket.new() or socket.bind() fail.
	-- @see socket.new
	-- @see socket.bind
	function bind.new(proto, ifindex)
	local proto = proto or ETH_P_ALL
	local ifindex = ifindex or 0
	local s = socket.new(af.PACKET, sock.RAW, proto)
	s:bind(string.pack(">H", proto), ifindex)
	return s
	end

if we will have only one method for creating a new raw socket, I'd keep that simpler and avoid the factory..

[sneaky-potato]

resolved in latest push

[sneaky-potato]

Hi @lneto
Sorry I missed the calling signature, examples lldpd.lua and tap.lua do not work because of that

Also I believe we need to call bind() differently when using both proto, ifindex vs only ifindex. I will create a quick pull request with working examples.