dtls_client: don't force the use of IPv6

Default to connecting to "localhost", like ssl_client1.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/programs/ssl/dtls_client.c b/programs/ssl/dtls_client.c
index 903b28d..8d7378a 100644
--- a/programs/ssl/dtls_client.c
+++ b/programs/ssl/dtls_client.c
@@ -44,7 +44,7 @@
 #ifdef FORCE_IPV4
 #define SERVER_ADDR "127.0.0.1"     /* Forces IPv4 */
 #else
-#define SERVER_ADDR "::1"
+#define SERVER_ADDR SERVER_NAME
 #endif
 
 #define MESSAGE     "Echo this"