ofproto-dpif-xlate: Stop forwarding MLD reports to group ports.

According with rfc4541 section 2.1.1, a snooping switch
should forward membership reports only to ports with
routers attached.The current code violates the RFC
forwarding membership reports to group ports as well.
The same issue doesn't exist with IPv4.

Fixes: 06994f8 ("mcast-snooping: Add Multicast Listener Discovery support")
Signed-off-by: XiaoXiong Ding <dingxiaoxiong@huawei.com>
Acked-by: Flavio Leitner <fbl@sysclose.org>
Signed-off-by: Ilya Maximets <i.maximets@ovn.org>

ofproto/ofproto-dpif-xlate.c

@@ -3043,6 +3043,7 @@ xlate_normal(struct xlate_ctx *ctx)
                 xlate_report(ctx, OFT_DETAIL, "MLD query, flooding");
                 xlate_normal_flood(ctx, in_xbundle, &xvlan);
             }
+            return;
         } else {
             if (is_ip_local_multicast(flow, wc)) {
                 /* RFC4541: section 2.1.2, item 2: Packets with a dst IP