tcp: update also tcp_output with regard to RFC 5681

Thanks to Ilpo Jarvinen, this updates also the initial window
setting for tcp_output with regard to RFC 5681.
Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/tcp_output.c

@@ -224,16 +224,10 @@ void tcp_select_initial_window(int __space, __u32 mss,
 		}
 	}
 
-	/* Set initial window to value enough for senders,
-	 * following RFC2414. Senders, not following this RFC,
-	 * will be satisfied with 2.
-	 */
+	/* Set initial window to value enough for senders, following RFC5681. */
 	if (mss > (1 << *rcv_wscale)) {
-		int init_cwnd = 4;
-		if (mss > 1460 * 3)
-			init_cwnd = 2;
-		else if (mss > 1460)
-			init_cwnd = 3;
+		int init_cwnd = rfc3390_bytes_to_packets(mss);
+
 		/* when initializing use the value from init_rcv_wnd
 		 * rather than the default from above
 		 */