[TCP]: Add tcp_available_congestion_control sysctl.

Create /proc/sys/net/ipv4/tcp_available_congestion_control
that reflects currently available TCP choices.

Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/net/tcp.h b/include/net/tcp.h
index 246916c..6af4baf 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -620,6 +620,9 @@
  * Interface for adding new TCP congestion control handlers
  */
 #define TCP_CA_NAME_MAX	16
+#define TCP_CA_MAX	128
+#define TCP_CA_BUF_MAX	(TCP_CA_NAME_MAX*TCP_CA_MAX)
+
 struct tcp_congestion_ops {
 	struct list_head	list;
 
@@ -659,6 +662,7 @@
 extern void tcp_cleanup_congestion_control(struct sock *sk);
 extern int tcp_set_default_congestion_control(const char *name);
 extern void tcp_get_default_congestion_control(char *name);
+extern void tcp_get_available_congestion_control(char *buf, size_t len);
 extern int tcp_set_congestion_control(struct sock *sk, const char *name);
 extern void tcp_slow_start(struct tcp_sock *tp);