macvlan: fix macvlan_get_size()

commit df8ef8f3aa (macvlan: add FDB bridge ops and macvlan flags)
forgot to update macvlan_get_size() after the addition of
IFLA_MACVLAN_FLAGS

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: John Fastabend <john.r.fastabend@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/macvlan.c

@@ -822,7 +822,10 @@ static int macvlan_changelink(struct net_device *dev,
 
 static size_t macvlan_get_size(const struct net_device *dev)
 {
-	return nla_total_size(4);
+	return (0
+		+ nla_total_size(4) /* IFLA_MACVLAN_MODE */
+		+ nla_total_size(2) /* IFLA_MACVLAN_FLAGS */
+		);
 }
 
 static int macvlan_fill_info(struct sk_buff *skb,