tcp: fix corner case issue in segmentation during rexmitting

If cur_mss grew very recently so that the previously G/TSOed skb
now fits well into a single segment it would get send up in
parts unless we calculate # of segments again. This corner-case
could happen eg. after mtu probe completes or less than
previously sack blocks are required for the opposite direction.
Signed-off-by: NIlpo Järvinen <ilpo.jarvinen@helsinki.fi>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv4/tcp_output.c

@@ -1921,6 +1921,8 @@ int tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb)
 	if (skb->len > cur_mss) {
 		if (tcp_fragment(sk, skb, cur_mss, cur_mss))
 			return -ENOMEM; /* We'll try again later. */
+	} else {
+		tcp_init_tso_segs(sk, skb, cur_mss);
 	}
 
 	tcp_retrans_try_collapse(sk, skb, cur_mss);