Import IPv6-supported Lua5.2 compatible code from Matthew Wild's repo

Signed-off-by: Vadim A. Misbakh-Soloviov <mva@mva.name>

samples/echosrvr.lua

@@ -0,0 +1,29 @@
+-----------------------------------------------------------------------------
+-- UDP sample: echo protocol server
+-- LuaSocket sample files
+-- Author: Diego Nehab
+-- RCS ID: $Id: echosrvr.lua,v 1.12 2005/11/22 08:33:29 diego Exp $
+-----------------------------------------------------------------------------
+local socket = require("socket")
+host = host or "127.0.0.1"
+port = port or 7
+if arg then
+    host = arg[1] or host
+    port = arg[2] or port
+end
+print("Binding to host '" ..host.. "' and port " ..port.. "...")
+udp = assert(socket.udp())
+assert(udp:setsockname(host, port))
+assert(udp:settimeout(5))
+ip, port = udp:getsockname()
+assert(ip, port)
+print("Waiting packets on " .. ip .. ":" .. port .. "...")
+while 1 do
+	dgram, ip, port = udp:receivefrom()
+	if dgram then
+		print("Echoing '" .. dgram .. "' to " .. ip .. ":" .. port)
+		udp:sendto(dgram, ip, port)
+	else
+        print(ip)
+    end
+end