tcp: account SYN-ACK timeouts & retransmissions

Currently we don't increment SYN-ACK timeouts & retransmissions
although we do increment the same stats for SYN. We seem to have lost
the SYN-ACK accounting with the introduction of tcp_syn_recv_timer
(commit 2248761e in the netdev-vger-cvs tree).

This patch fixes this issue. In the process we also rename the v4/v6
syn/ack retransmit functions for clarity. We also add a new
request_socket operations (syn_ack_timeout) so we can keep code in
inet_connection_sock.c protocol agnostic.

Signed-off-by: Octavian Purdila <opurdila@ixiacom.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 c9b50eb..99e6e19 100644
--- a/include/net/request_sock.h
+++ b/include/net/request_sock.h
@@ -45,6 +45,8 @@
 	void		(*send_reset)(struct sock *sk,
 				      struct sk_buff *skb);
 	void		(*destructor)(struct request_sock *req);
+	void		(*syn_ack_timeout)(struct sock *sk,
+					   struct request_sock *req);
 };
 
 /* struct request_sock - mini sock to represent a connection request