[NET] sysctl: make sysctl_somaxconn per-namespace

Just move the variable on the struct net and adjust
its usage.

Others sysctls from sys.net.core table are more
difficult to virtualize (i.e. make them per-namespace),
but I'll look at them as well a bit later.

Signed-off-by: Pavel Emelyanov <xemul@oenvz.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/socket.c b/net/socket.c
index 9ebca5c..7651de0 100644
--- a/net/socket.c
+++ b/net/socket.c
@@ -1365,17 +1365,17 @@
  *	ready for listening.
  */
 
-int sysctl_somaxconn __read_mostly = SOMAXCONN;
-
 asmlinkage long sys_listen(int fd, int backlog)
 {
 	struct socket *sock;
 	int err, fput_needed;
+	int somaxconn;
 
 	sock = sockfd_lookup_light(fd, &err, &fput_needed);
 	if (sock) {
-		if ((unsigned)backlog > sysctl_somaxconn)
-			backlog = sysctl_somaxconn;
+		somaxconn = sock->sk->sk_net->sysctl_somaxconn;
+		if ((unsigned)backlog > somaxconn)
+			backlog = somaxconn;
 
 		err = security_socket_listen(sock, backlog);
 		if (!err)