tcp: Add tcp_retransmit_time() helper routine

[Jon Maxwell <jmaxwell37@gmail.com>]

Create a seperate helper routine as per Neal Cardwells suggestion. To 
be used by the final commit in this series and retransmits_timed_out().

Signed-off-by: Jon Maxwell <jmaxwell37@gmail.com>
---
 net/ipv4/tcp_timer.c | 25 +++++++++++++++++--------
 1 file changed, 17 insertions(+), 8 deletions(-)

diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c
index fa34984d0b12..d212f183dd2d 100644
--- a/net/ipv4/tcp_timer.c
+++ b/net/ipv4/tcp_timer.c
@@ -22,6 +22,20 @@
 #include <linux/gfp.h>
 #include <net/tcp.h>
 
+u32 tcp_retransmit_stamp(const struct sock *sk)
+{
+	u32 start_ts = tcp_sk(sk)->retrans_stamp;
+
+	if (unlikely(!start_ts)) {
+		struct sk_buff *head = tcp_rtx_queue_head(sk);
+
+		if (!head)
+			return 0;
+		start_ts = tcp_skb_timestamp(head);
+	}
+	return start_ts;
+}
+
 /**
  *  tcp_write_err() - close socket and save error info
  *  @sk:  The socket the error has appeared on.
@@ -166,14 +180,9 @@ static bool retransmits_timed_out(struct sock *sk,
 	if (!inet_csk(sk)->icsk_retransmits)
 		return false;
 
-	start_ts = tcp_sk(sk)->retrans_stamp;
-	if (unlikely(!start_ts)) {
-		struct sk_buff *head = tcp_rtx_queue_head(sk);
-
-		if (!head)
-			return false;
-		start_ts = tcp_skb_timestamp(head);
-	}
+	start_ts = tcp_retransmit_stamp(sk);
+	if (!start_ts)
+		return false;
 
 	if (likely(timeout == 0)) {
 		linear_backoff_thresh = ilog2(TCP_RTO_MAX/rto_base);
-- 
2.13.6