ipv4: Use FIELD_SIZEOF() in inet_init().

Signed-off-by: YOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/af_inet.c

@@ -1705,12 +1705,11 @@ static struct packet_type ip_packet_type __read_mostly = {
 
 static int __init inet_init(void)
 {
-	struct sk_buff *dummy_skb;
 	struct inet_protosw *q;
 	struct list_head *r;
 	int rc = -EINVAL;
 
-	BUILD_BUG_ON(sizeof(struct inet_skb_parm) > sizeof(dummy_skb->cb));
+	BUILD_BUG_ON(sizeof(struct inet_skb_parm) > FIELD_SIZEOF(struct sk_buff, cb));
 
 	sysctl_local_reserved_ports = kzalloc(65536 / 8, GFP_KERNEL);
 	if (!sysctl_local_reserved_ports)