Dual DTLS version methods.

Add new methods DTLS_*_method() which support both DTLS 1.0 and DTLS 1.2 and
pick the highest version the peer supports during negotiation.

As with SSL/TLS options can change this behaviour specifically
SSL_OP_NO_DTLSv1 and SSL_OP_NO_DTLSv1_2.

ssl/ssl.h

diff --git a/ssl/ssl.h b/ssl/ssl.h
index 7072c2f..cba5f4d 100644
--- a/ssl/ssl.h
+++ b/ssl/ssl.h
@@ -617,6 +617,9 @@
 #define SSL_OP_NO_TLSv1_2				0x08000000L
 #define SSL_OP_NO_TLSv1_1				0x10000000L
 
+#define SSL_OP_NO_DTLSv1				0x04000000L
+#define SSL_OP_NO_DTLSv1_2				0x08000000L
+
 #define SSL_OP_NO_SSL_MASK (SSL_OP_NO_SSLv2|SSL_OP_NO_SSLv3|\
 	SSL_OP_NO_TLSv1|SSL_OP_NO_TLSv1_1|SSL_OP_NO_TLSv1_2)
 
@@ -2115,6 +2118,10 @@
 const SSL_METHOD *DTLSv1_2_server_method(void);	/* DTLSv1.2 */
 const SSL_METHOD *DTLSv1_2_client_method(void);	/* DTLSv1.2 */
 
+const SSL_METHOD *DTLS_method(void);		/* DTLS 1.0 and 1.2 */
+const SSL_METHOD *DTLS_server_method(void);	/* DTLS 1.0 and 1.2 */
+const SSL_METHOD *DTLS_client_method(void);	/* DTLS 1.0 and 1.2 */
+
 STACK_OF(SSL_CIPHER) *SSL_get_ciphers(const SSL *s);
 
 int SSL_do_handshake(SSL *s);