If we receive an "update_requested" KeyUpdate then respond with a KeyUpdate

Reviewed-by: Rich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/2609)
diff --git a/ssl/statem/statem_clnt.c b/ssl/statem/statem_clnt.c
index ced3317..909b2f0 100644
--- a/ssl/statem/statem_clnt.c
+++ b/ssl/statem/statem_clnt.c
@@ -439,6 +439,12 @@
         return WRITE_TRAN_CONTINUE;
 
     case TLS_ST_CR_KEY_UPDATE:
+        if (s->key_update != SSL_KEY_UPDATE_NONE) {
+            st->hand_state = TLS_ST_CW_KEY_UPDATE;
+            return WRITE_TRAN_CONTINUE;
+        }
+        /* Fall through */
+
     case TLS_ST_CW_KEY_UPDATE:
     case TLS_ST_CR_SESSION_TICKET:
     case TLS_ST_CW_FINISHED: