[TCP] FRTO: Incorrectly clears TCPCB_EVER_RETRANS bit

FRTO was slightly too brave... Should only clear
TCPCB_SACKED_RETRANS bit.
Signed-off-by: NIlpo Järvinen <ilpo.jarvinen@helsinki.fi>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv4/tcp_input.c

@@ -1266,7 +1266,7 @@ void tcp_enter_frto(struct sock *sk)
 	tp->undo_retrans = 0;
 
 	sk_stream_for_retrans_queue(skb, sk) {
-		TCP_SKB_CB(skb)->sacked &= ~TCPCB_RETRANS;
+		TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
 	}
 	tcp_sync_left_out(tp);