net: bridge: add compile-time assert for cb struct size

make build fail if structure no longer fits into ->cb storage.
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/bridge/br.c

@@ -190,6 +190,8 @@ static int __init br_init(void)
 {
 	int err;
 
+	BUILD_BUG_ON(sizeof(struct br_input_skb_cb) > FIELD_SIZEOF(struct sk_buff, cb));
+
 	err = stp_proto_register(&br_stp_proto);
 	if (err < 0) {
 		pr_err("bridge: can't register sap for STP\n");