tcp: Make TCP_MAXSEG minimum more correct.

Use TCP_MIN_MSS instead of constant 64.

Reported-by: Min Zhang <mzhang@mvista.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 0814199..f15c36a 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -2246,7 +2246,7 @@
 		/* Values greater than interface MTU won't take effect. However
 		 * at the point when this call is done we typically don't yet
 		 * know which interface is going to be used */
-		if (val < 64 || val > MAX_TCP_WINDOW) {
+		if (val < TCP_MIN_MSS || val > MAX_TCP_WINDOW) {
 			err = -EINVAL;
 			break;
 		}