Fix dtls listen on ipv6 with default ip

IP adress always defaulted to {0,0,0,0} even for ipv6 connections,
which caused a single entry if you where listening on both stacks.

Fixes erlang#7955

lib/ssl/src/dtls_socket.erl

@@ -51,7 +51,11 @@ listen(Port, #config{inet_ssl = SockOpts,
                      ssl = SslOpts,
                      emulated = EmOpts,
                      inet_user = Options} = Config) ->
-    IP = proplists:get_value(ip, SockOpts, {0,0,0,0}),
+    DefIP = case proplists:get_value(inet6, SockOpts, false) of
+                false -> {0,0,0,0};
+                true -> {0,0,0,0, 0,0,0,0}
+            end,
+    IP = proplists:get_value(ip, SockOpts, DefIP),
     case dtls_listener_sup:lookup_listener(IP, Port) of
         undefined ->
             start_new_listener(IP, Port, Config);
@@ -96,10 +100,14 @@ connect(Address, Port, #config{transport_info = {Transport, _, _, _, _} = CbInfo
 
 close(#sslsocket{pid = {dtls, #config{dtls_handler = {Pid, Port0},
                                       inet_ssl = SockOpts}}}) ->
-    IP = proplists:get_value(ip, SockOpts, {0,0,0,0}),
+    DefIP = case proplists:get_value(inet6, SockOpts, false) of
+                false -> {0,0,0,0};
+                true  -> {0,0,0,0, 0,0,0,0}
+            end,
+    IP = proplists:get_value(ip, SockOpts, DefIP),
     Port = get_real_port(Pid, Port0),
     dtls_listener_sup:register_listener({undefined, Pid}, IP, Port),
-    dtls_packet_demux:close(Pid).   
+    dtls_packet_demux:close(Pid).
 
 close(_, dtls) ->
     ok;