ipv4: Raise tcp PMTU probe mss base size

Quotes from RFC4821 7.2.  Selecting Initial Values

   It is RECOMMENDED that search_low be initially set to an MTU size
   that is likely to work over a very wide range of environments.  Given
   today's technologies, a value of 1024 bytes is probably safe enough.
   The initial value for search_low SHOULD be configurable.

Moreover, set a small value will introduce extra time for the search
to converge. So set the initial probe base mss size to 1024 Bytes.

Signed-off-by: Fan Du <fan.du@intel.com>
Acked-by: John Heffner <johnwheffner@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/tcp.h

diff --git a/include/net/tcp.h b/include/net/tcp.h
index f87599d..834089b 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -65,7 +65,7 @@
 #define TCP_MIN_MSS		88U
 
 /* The least MTU to use for probing */
-#define TCP_BASE_MSS		512
+#define TCP_BASE_MSS		1024
 
 /* After receiving this amount of duplicate ACKs fast retransmit starts. */
 #define TCP_FASTRETRANS_THRESH 3