[TCP]: Tidy up skb_entail

Heck, it even saves us some few bytes:

[acme@newtoy net-2.6.20]$ codiff -f /tmp/tcp.o.before ../OUTPUT/qemu/net-2.6.20/net/ipv4/tcp.o
/pub/scm/linux/kernel/git/acme/net-2.6.20/net/ipv4/tcp.c:
  tcp_sendpage |   -7
  tcp_sendmsg  |   -5
 2 functions changed, 12 bytes removed
[acme@newtoy net-2.6.20]$
Signed-off-by: Arnaldo Carvalho de Melo <acme@mandriva.com>

net/ipv4/tcp.c

@@ -463,11 +463,12 @@ static inline int forced_push(struct tcp_sock *tp)
 static inline void skb_entail(struct sock *sk, struct tcp_sock *tp,
 			      struct sk_buff *skb)
 {
+	struct tcp_skb_cb *tcb = TCP_SKB_CB(skb);
+
 	skb->csum    = 0;
-	TCP_SKB_CB(skb)->seq = tp->write_seq;
-	TCP_SKB_CB(skb)->end_seq = tp->write_seq;
-	TCP_SKB_CB(skb)->flags = TCPCB_FLAG_ACK;
-	TCP_SKB_CB(skb)->sacked = 0;
+	tcb->seq     = tcb->end_seq = tp->write_seq;
+	tcb->flags   = TCPCB_FLAG_ACK;
+	tcb->sacked  = 0;
 	skb_header_release(skb);
 	__skb_queue_tail(&sk->sk_write_queue, skb);
 	sk_charge_skb(sk, skb);