Fix crash in ejabberd_c2s when blacklist hook returned true (thanks to Jonas Ådahl)

Cause of the crash jlib:ip_to_list/1 only supports IP tuples using the
form {N1,N2,N3,N4} which is not the case when IPv6 is enabled.

src/ejabberd_c2s.erl

@@ -243,8 +243,8 @@ init([{SockMod, Socket}, Opts, FSMLimitOpts]) ->
     %% Check if IP is blacklisted:
     case is_ip_blacklisted(IP) of
 	true ->
-	    ?INFO_MSG("Connection attempt from blacklisted IP: ~s",
-		      [jlib:ip_to_list(IP)]),
+	    ?INFO_MSG("Connection attempt from blacklisted IP: ~s (~w)",
+		      [jlib:ip_to_list(IP), IP]),
 	    {stop, normal};
 	false ->
 	    Socket1 =

src/jlib.erl

@@ -387,8 +387,8 @@ e(X) ->                     exit({bad_encode_base64_token, X}).
 %% Convert Erlang inet IP to list
 ip_to_list({IP, _Port}) ->
     ip_to_list(IP);
-ip_to_list({A,B,C,D}) ->
-    lists:flatten(io_lib:format("~w.~w.~w.~w",[A,B,C,D])).
+ip_to_list(IpTuple) when is_tuple(IpTuple) ->
+    inet_parse:ntoa(IpTuple).
 
 % --------------------------------------------------------------------
 % Compat layer.