ipv6/ila: fix nlsize calculation for lwtunnel

The handler 'ila_fill_encap_info' adds one attribute: ILA_ATTR_LOCATOR.

Fixes: 65d7ab8d ("net: Identifier Locator Addressing module")
CC: Tom Herbert <tom@herbertland.com>
Signed-off-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv6/ila/ila_lwt.c

@@ -120,8 +120,7 @@ static int ila_fill_encap_info(struct sk_buff *skb,
 
 static int ila_encap_nlsize(struct lwtunnel_state *lwtstate)
 {
-	/* No encapsulation overhead */
-	return 0;
+	return nla_total_size(sizeof(u64)); /* ILA_ATTR_LOCATOR */
 }
 
 static int ila_encap_cmp(struct lwtunnel_state *a, struct lwtunnel_state *b)