tcp: doc : fix the syncookies default value

syncookies is on for default since in commit e994b7c (tcp: Don't make syn cookies initial setting depend on CONFIG_SYSCTL). And fix a typo of CONFIG_SYN_COOKIES. Signed-off-by: Shan Wei <davidshan@tencent.com> Signed-off-by: David S. Miller <davem@davemloft.net>

Author: shanwei

Documentation/networking/ip-sysctl.txt

@@ -420,10 +420,10 @@ tcp_synack_retries - INTEGER
 for a passive TCP connection will happen after 63seconds.
 
 tcp_syncookies - BOOLEAN
-Only valid when the kernel was compiled with CONFIG_SYNCOOKIES
+Only valid when the kernel was compiled with CONFIG_SYN_COOKIES
 Send out syncookies when the syn backlog queue of a socket
 overflows. This is to prevent against the common 'SYN flood attack'
-Default: FALSE
+Default: 1
 
 Note, that syncookies is fallback facility.
 It MUST NOT be used to help highly loaded servers to stand