tcp: sizeof struct tcp_skb_cb is 44

Correct comment stating sizeof(struct tcp_skb_cb) is 36 or 40, since its
44 bytes, since commit 951dbc8ac714b04 ([IPV6]: Move nextheader offset
to the IP6CB).

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/tcp.h

@@ -570,11 +570,10 @@ extern u32 __tcp_select_window(struct sock *sk);
 #define TCPHDR_CWR 0x80
 
 /* This is what the send packet queuing engine uses to pass
- * TCP per-packet control information to the transmission
- * code.  We also store the host-order sequence numbers in
- * here too.  This is 36 bytes on 32-bit architectures,
- * 40 bytes on 64-bit machines, if this grows please adjust
- * skbuff.h:skbuff->cb[xxx] size appropriately.
+ * TCP per-packet control information to the transmission code.
+ * We also store the host-order sequence numbers in here too.
+ * This is 44 bytes if IPV6 is enabled.
+ * If this grows please adjust skbuff.h:skbuff->cb[xxx] size appropriately.
  */
 struct tcp_skb_cb {
 	union {