net: Correct type of tcp_syncookies sysctl.

It can take on the values of '0', '1', and '2' and thus
is not a boolean.
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Documentation/networking/ip-sysctl.txt

@@ -603,7 +603,7 @@ tcp_synack_retries - INTEGER
 	with the current initial RTO of 1second. With this the final timeout
 	for a passive TCP connection will happen after 63seconds.
 
-tcp_syncookies - BOOLEAN
+tcp_syncookies - INTEGER
 	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'