amt: drop unexpected multicast data

AMT gateway interface should not receive unexpected multicast data.
Multicast data message type should be received after sending an update
message, which means all establishment between gateway and relay is
finished.
So, amt_multicast_data_handler() checks amt->status.

Fixes: cbc21dc1 ("amt: add data plane of amt interface")
Signed-off-by: Taehee Yoo <ap420073@gmail.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

drivers/net/amt.c

@@ -2282,6 +2282,9 @@ static bool amt_multicast_data_handler(struct amt_dev *amt, struct sk_buff *skb)
 	struct ethhdr *eth;
 	struct iphdr *iph;
 
+	if (READ_ONCE(amt->status) != AMT_STATUS_SENT_UPDATE)
+		return true;
+
 	hdr_size = sizeof(*amtmd) + sizeof(struct udphdr);
 	if (!pskb_may_pull(skb, hdr_size))
 		return true;