syncookies: do not store rcv_wscale in tcp timestamp

As pointed out by Fernando Gont there is no need to encode rcv_wscale
into the cookie.

We did not use the restored rcv_wscale anyway; it is recomputed
via tcp_select_initial_window().

Thus we can save 4 bits in the ts option space by removing rcv_wscale.
In case window scaling was not supported, we set the (invalid) wscale
value 0xf.

Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv6/syncookies.c

@@ -217,7 +217,6 @@ struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb)
 	req->retrans = 0;
 	ireq->ecn_ok		= 0;
 	ireq->snd_wscale	= tcp_opt.snd_wscale;
-	ireq->rcv_wscale	= tcp_opt.rcv_wscale;
 	ireq->sack_ok		= tcp_opt.sack_ok;
 	ireq->wscale_ok		= tcp_opt.wscale_ok;
 	ireq->tstamp_ok		= tcp_opt.saw_tstamp;