netfilter: nf_ct_tcp: don't scale the size of the window up twice

For a picked up connection, the window win is scaled twice: one is by the
initialization code, and the other is by the sender updating code.

I use the temporary variable swin instead of modifying the variable win.
Signed-off-by: Changli Gao <xiaosuo@gmail.com>
Acked-by: Jozsef Kadlecsik <kadlec@blackhole.kfki.hu>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/nf_conntrack_proto_tcp.c

@@ -584,8 +584,8 @@ static bool tcp_in_window(const struct nf_conn *ct,
 			 * Let's try to use the data from the packet.
 			 */
 			sender->td_end = end;
-			win <<= sender->td_scale;
-			sender->td_maxwin = (win == 0 ? 1 : win);
+			swin = win << sender->td_scale;
+			sender->td_maxwin = (swin == 0 ? 1 : swin);
 			sender->td_maxend = end + sender->td_maxwin;
 			/*
 			 * We haven't seen traffic in the other direction yet