[TCP]: lower stack usage in cookie_hash() function

400 bytes allocated on stack might be a litle bit too much. Using a
per_cpu var is more friendly.
Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>
Signed-off-by: YOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>

net/ipv4/syncookies.c

@@ -35,10 +35,12 @@ module_init(init_syncookies);
 #define COOKIEBITS 24	/* Upper bits store count */
 #define COOKIEMASK (((__u32)1 << COOKIEBITS) - 1)
 
+static DEFINE_PER_CPU(__u32, cookie_scratch)[16 + 5 + SHA_WORKSPACE_WORDS];
+
 static u32 cookie_hash(__be32 saddr, __be32 daddr, __be16 sport, __be16 dport,
 		       u32 count, int c)
 {
-	__u32 tmp[16 + 5 + SHA_WORKSPACE_WORDS];
+	__u32 *tmp = __get_cpu_var(cookie_scratch);
 
 	memcpy(tmp + 3, syncookie_secret[c], sizeof(syncookie_secret[c]));
 	tmp[0] = (__force u32)saddr;