[TCP]: Limit processing lost_retrans loop to work-to-do cases

This addition of lost_retrans_low to tcp_sock might be
unnecessary, it's not clear how often lost_retrans worker is
executed when there wasn't work to do.

Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/linux/tcp.h b/include/linux/tcp.h
index 9ff456e..c5b94c1 100644
--- a/include/linux/tcp.h
+++ b/include/linux/tcp.h
@@ -348,6 +348,8 @@
 	int     lost_cnt_hint;
 	int     retransmit_cnt_hint;
 
+	u32	lost_retrans_low;	/* Sent seq after any rxmit (lowest) */
+
 	u16	advmss;		/* Advertised MSS			*/
 	u16	prior_ssthresh; /* ssthresh saved at recovery start	*/
 	u32	lost_out;	/* Lost packets			*/