ipv4: Namespaceify tcp_max_syn_backlog knob

Different namespace application might require different maximal
number of remembered connection requests.

Signed-off-by: Haishuang Yan <yanhaishuang@cmss.chinamobile.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/net/request_sock.h b/include/net/request_sock.h
index 6ebe13e..a12a5d2 100644
--- a/include/net/request_sock.h
+++ b/include/net/request_sock.h
@@ -1,7 +1,7 @@
 /*
  * NET		Generic infrastructure for Network protocols.
  *
- *		Definitions for request_sock 
+ *		Definitions for request_sock
  *
  * Authors:	Arnaldo Carvalho de Melo <acme@conectiva.com.br>
  *
@@ -123,8 +123,6 @@ static inline void reqsk_put(struct request_sock *req)
 		reqsk_free(req);
 }
 
-extern int sysctl_max_syn_backlog;
-
 /*
  * For a TCP Fast Open listener -
  *	lock - protects the access to all the reqsk, which is co-owned by