Only call ssl3_init_finished_mac once for DTLS

In DTLS if an IO retry occurs during writing of a fragmented ClientHello
then we can end up reseting the finish mac variables on the retry, which
causes a handshake failure. We should only reset on the first attempt not
on retries.

Thanks to BoringSSL for reporting this issue.

RT#4119

Reviewed-by: Tim Hudson <tjh@openssl.org>
(cherry picked from commit 15a7164eb7)

ssl/d1_clnt.c

@@ -299,13 +299,12 @@ int dtls1_connect(SSL *s)
 #endif
 
         case SSL3_ST_CW_CLNT_HELLO_A:
-        case SSL3_ST_CW_CLNT_HELLO_B:
-
             s->shutdown = 0;
 
             /* every DTLS ClientHello resets Finished MAC */
             ssl3_init_finished_mac(s);
 
+        case SSL3_ST_CW_CLNT_HELLO_B:
             dtls1_start_timer(s);
             ret = dtls1_client_hello(s);
             if (ret <= 0)