[TCP] MIB: Count FRTO's successfully detected spurious RTOs

Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 4866e75e..4b27739 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -2935,6 +2935,7 @@
 		}
 		tp->frto_counter = 0;
 		tp->undo_marker = 0;
+		NET_INC_STATS_BH(LINUX_MIB_TCPSPURIOUSRTOS);
 	}
 	return 0;
 }