ip_tunnel: Fix off-by-one error in forming dev name.

As Ben pointed out following patch fixes bug in checking device
name length limits while forming tunnel device name.

CC: Ben Hutchings <bhutchings@solarflare.com>
Signed-off-by: Pravin B Shelar <pshelar@nicira.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/ip_tunnel.c b/net/ipv4/ip_tunnel.c
index 9d96b68..e4147ec 100644
--- a/net/ipv4/ip_tunnel.c
+++ b/net/ipv4/ip_tunnel.c
@@ -284,7 +284,7 @@
 	if (parms->name[0])
 		strlcpy(name, parms->name, IFNAMSIZ);
 	else {
-		if (strlen(ops->kind) + 3 >= IFNAMSIZ) {
+		if (strlen(ops->kind) > (IFNAMSIZ - 3)) {
 			err = -E2BIG;
 			goto failed;
 		}