tcp: properly account Fast Open SYN-ACK retrans

Since the TFO socket is accepted right off SYN-data, the socket
owner can call getsockopt(TCP_INFO) to collect ongoing SYN-ACK
retransmission or timeout stats (i.e., tcpi_total_retrans,
tcpi_retransmits). Currently those stats are only updated
upon handshake completes. This patch fixes it.

Signed-off-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: Soheil Hassas Yeganeh <soheil@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c
index d84930b..f712b41 100644
--- a/net/ipv4/tcp_timer.c
+++ b/net/ipv4/tcp_timer.c
@@ -384,6 +384,7 @@
 	 */
 	inet_rtx_syn_ack(sk, req);
 	req->num_timeout++;
+	icsk->icsk_retransmits++;
 	inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
 			  TCP_TIMEOUT_INIT << req->num_timeout, TCP_RTO_MAX);
 }