net: use common macro for assering skb->cb[] available size in protocol families

As part of an effort to move skb->dropcount to skb->cb[] use a common
macro in protocol families using skb->cb[] for ancillary data to
validate available room in skb->cb[].

Signed-off-by: Eyal Birger <eyal.birger@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/af_inet.c b/net/ipv4/af_inet.c
index d2e49ba..4ce954c 100644
--- a/net/ipv4/af_inet.c
+++ b/net/ipv4/af_inet.c
@@ -1675,7 +1675,7 @@
 	struct list_head *r;
 	int rc = -EINVAL;
 
-	BUILD_BUG_ON(sizeof(struct inet_skb_parm) > FIELD_SIZEOF(struct sk_buff, cb));
+	sock_skb_cb_check_size(sizeof(struct inet_skb_parm));
 
 	rc = proto_register(&tcp_prot, 1);
 	if (rc)
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 9d72a0f..4b57ea8 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -3005,12 +3005,11 @@
 
 void __init tcp_init(void)
 {
-	struct sk_buff *skb = NULL;
 	unsigned long limit;
 	int max_rshare, max_wshare, cnt;
 	unsigned int i;
 
-	BUILD_BUG_ON(sizeof(struct tcp_skb_cb) > sizeof(skb->cb));
+	sock_skb_cb_check_size(sizeof(struct tcp_skb_cb));
 
 	percpu_counter_init(&tcp_sockets_allocated, 0, GFP_KERNEL);
 	percpu_counter_init(&tcp_orphan_count, 0, GFP_KERNEL);