[IPV4]: Fix ip_queue_xmit identity increment for TSO packets

When ip_queue_xmit calls ip_select_ident_more for IP identity selection
it gives it the wrong packet count for TSO packets.  The ip_select_*
functions expect one less than the number of packets, so we need to
subtract one for TSO packets.

This bug was diagnosed and fixed by Tom Young.
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/ip_output.c

@@ -353,7 +353,8 @@ packet_routed:
 		ip_options_build(skb, opt, inet->daddr, rt, 0);
 	}
 
-	ip_select_ident_more(iph, &rt->u.dst, sk, skb_shinfo(skb)->tso_segs);
+	ip_select_ident_more(iph, &rt->u.dst, sk,
+			     (skb_shinfo(skb)->tso_segs ?: 1) - 1);
 
 	/* Add an IP checksum. */
 	ip_send_check(iph);