[TCP/DCCP]: Introduce net_xmit_eval

Throughout the TCP/DCCP (and tunnelling) code, it often happens that the
return code of a transmit function needs to be tested against NET_XMIT_CN
which is a value that does not indicate a strict error condition.

This patch uses a macro for these recurring situations which is consistent
with the already existing macro net_xmit_errno, saving on duplicated code.

Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
Signed-off-by: Arnaldo Carvalho de Melo <acme@mandriva.com>
diff --git a/net/ipv6/ip6_tunnel.c b/net/ipv6/ip6_tunnel.c
index 4919f92..80a1190 100644
--- a/net/ipv6/ip6_tunnel.c
+++ b/net/ipv6/ip6_tunnel.c
@@ -748,7 +748,7 @@
 	err = NF_HOOK(PF_INET6, NF_IP6_LOCAL_OUT, skb, NULL, 
 		      skb->dst->dev, dst_output);
 
-	if (err == NET_XMIT_SUCCESS || err == NET_XMIT_CN) {
+	if (net_xmit_eval(err) == 0) {
 		stats->tx_bytes += pkt_len;
 		stats->tx_packets++;
 	} else {