net: TCP_MSS_DEFAULT, TCP_MSS_DESIRED

Define two symbols needed in both kernel and user space.

Remove old (somewhat incorrect) kernel variant that wasn't used in
most cases.  Default should apply to both RMSS and SMSS (RFC2581).

Replace numeric constants with defined symbols.

Stand-alone patch, originally developed for TCPCT.

Signed-off-by: William.Allen.Simpson@gmail.com
Acked-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 657ae33..cf7f208 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -217,7 +217,7 @@
 	if (inet->opt)
 		inet_csk(sk)->icsk_ext_hdr_len = inet->opt->optlen;
 
-	tp->rx_opt.mss_clamp = 536;
+	tp->rx_opt.mss_clamp = TCP_MSS_DEFAULT;
 
 	/* Socket identity is still unknown (sport may be zero).
 	 * However we set state to SYN-SENT and not releasing socket
@@ -1268,7 +1268,7 @@
 		goto drop_and_free;
 
 	tcp_clear_options(&tmp_opt);
-	tmp_opt.mss_clamp = 536;
+	tmp_opt.mss_clamp = TCP_MSS_DEFAULT;
 	tmp_opt.user_mss  = tcp_sk(sk)->rx_opt.user_mss;
 
 	tcp_parse_options(skb, &tmp_opt, 0, dst);
@@ -1815,7 +1815,7 @@
 	 */
 	tp->snd_ssthresh = TCP_INFINITE_SSTHRESH;
 	tp->snd_cwnd_clamp = ~0;
-	tp->mss_cache = 536;
+	tp->mss_cache = TCP_MSS_DEFAULT;
 
 	tp->reordering = sysctl_tcp_reordering;
 	icsk->icsk_ca_ops = &tcp_init_congestion_ops;