dtls_get_message changes for state machine move

Create a dtls_get_message function similar to the old dtls1_get_message but
in the format required for the new state machine code. The old function will
eventually be deleted in later commits.

Reviewed-by: Tim Hudson <tjh@openssl.org>
Reviewed-by: Richard Levitte <levitte@openssl.org>

ssl/statem.c

diff --git a/ssl/statem.c b/ssl/statem.c
index 2ebe2a6..f1df6a3 100644
--- a/ssl/statem.c
+++ b/ssl/statem.c
@@ -464,7 +464,14 @@
         case READ_STATE_HEADER:
             s->init_num = 0;
             /* Get the state the peer wants to move to */
-            ret = tls_get_message_header(s, &mt);
+            if (SSL_IS_DTLS(s)) {
+                /*
+                 * In DTLS we get the whole message in one go - header and body
+                 */
+                ret = dtls_get_message(s, &mt, &len);
+            } else {
+                ret = tls_get_message_header(s, &mt);
+            }
 
             if (ret == 0) {
                 /* Could be non-blocking IO */