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

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

samples/mcsend.lua

@@ -0,0 +1,20 @@
+local socket = require"socket"
+local group = "225.0.0.37"
+local port = 12345
+local c = assert(socket.udp())
+--print(assert(c:setoption("reuseport", true)))
+--print(assert(c:setsockname("*", port)))
+--print(assert(c:setoption("ip-multicast-loop", false)))
+--print(assert(c:setoption("ip-multicast-ttl", 4)))
+--print(assert(c:setoption("ip-multicast-if", "10.0.1.3")))
+--print(assert(c:setoption("ip-add-membership", {multiaddr = group, interface = "*"})))
+local i = 0
+while 1 do
+    local message = string.format("hello all %d!", i)
+    assert(c:sendto(message, group, port))
+    print("sent " .. message)
+    socket.sleep(1)
+    c:settimeout(0.5)
+    print(c:receivefrom())
+    i = i + 1
+end