Use ipv4 when querying IP lookup service

Also, replace broken IP lookup service with some others

src/mtp_config.erl

@@ -261,8 +261,10 @@ http_get(Url) ->
     {ok, Vsn} = application:get_key(mtproto_proxy, vsn),
     UserAgent = "MTProtoProxy/" ++ Vsn ++ " (+https://github.com/seriyps/mtproto_proxy)",
     Headers = [{"User-Agent", UserAgent}],
+    %% XXX: ipfamily only works on OTP >= 20.3.4; see OTP 2dc08b47e6a5ea759781479593c55bb5776cd828
     {ok, {{_, 200, _}, _, Body}} =
-        httpc:request(get, {Url, Headers}, [{timeout, 3000}], []),
+        httpc:request(get, {Url, Headers}, [{timeout, 3000}],
+                      [{socket_opts, [{ipfamily, inet}]}]),
     {ok, Body}.
 
 random_choice(L) ->

src/mtproto_proxy.app.src

@@ -31,8 +31,9 @@
         %% 2nd one will be tried and so on
         {ip_lookup_services,
          ["http://ipv4.seriyps.ru/",
-          "https://digitalresistance.dog/myIp",
-          "http://ipv4.myexternalip.com/raw"]},
+          "http://v4.ident.me/",
+          "http://ipv4.icanhazip.com/",
+          "https://digitalresistance.dog/myIp"]},
         %% {external_ip, "YOUR.SERVER.EXTERNAL.IP"},
 
         %% Interface to listen for incoming connections