ejabberd_stun: Add 'turn_blacklist' option

The new 'turn_blacklist' listener option allows for specifying one or
more IP addresses and/or subnet addresses/masks.  The TURN server will
refuse to relay traffic from/to blacklisted IP addresses.  By default,
Teredo and 6to4 addresses are blacklisted, as mandated by RFC 6156
(section 9.1).

mix.exs

@@ -90,7 +90,7 @@ defmodule Ejabberd.Mixfile do
      {:stringprep, "~> 1.0"},
      {:fast_yaml, "~> 1.0"},
      {:fast_tls, "~> 1.1"},
-     {:stun, git: "https://github.com/processone/stun", ref: "481f4dbb8b5793659aedf44048d7c5fde968bfbb", override: true},
+     {:stun, git: "https://github.com/processone/stun", ref: "a96f588c8ded48cd15e99911cf7b22ca67b532db", override: true},
      {:esip, "~> 1.0.32"},
      {:p1_mysql, "~> 1.0"},
      {:mqtree, "~> 1.0"},

rebar.config

@@ -36,7 +36,7 @@
         {mqtree, ".*", {git, "https://github.com/processone/mqtree", {tag, "1.0.7"}}},
 	{p1_acme, ".*", {git, "https://github.com/processone/p1_acme.git", {tag, "1.0.5"}}},
         {base64url, ".*", {git, "https://github.com/dvv/base64url.git", {tag, "v1.0"}}},
-        {if_var_true, stun, {stun, ".*", {git, "https://github.com/processone/stun", "481f4dbb8b5793659aedf44048d7c5fde968bfbb"}}},
+        {if_var_true, stun, {stun, ".*", {git, "https://github.com/processone/stun", "a96f588c8ded48cd15e99911cf7b22ca67b532db"}}},
         {if_var_true, sip, {esip, ".*", {git, "https://github.com/processone/esip", {tag, "1.0.33"}}}},
         {if_var_true, mysql, {p1_mysql, ".*", {git, "https://github.com/processone/p1_mysql",
                                                {tag, "1.0.15"}}}},

src/ejabberd_stun.erl

@@ -177,6 +177,8 @@ listen_opt_type(turn_max_allocations) ->
     econf:pos_int(infinity);
 listen_opt_type(turn_max_permissions) ->
     econf:pos_int(infinity);
+listen_opt_type(turn_blacklist) ->
+    econf:list_or_single(econf:ip_mask());
 listen_opt_type(server_name) ->
     econf:binary();
 listen_opt_type(certfile) ->
@@ -195,5 +197,6 @@ listen_options() ->
      {turn_max_port, 65535},
      {turn_max_allocations, 10},
      {turn_max_permissions, 10},
+     {turn_blacklist, [<<"2001::/32">>, <<"2002::/16">>]}, % Teredo, 6to4.
      {server_name, <<"ejabberd">>}].
 -endif.