netfilter: ipv6: add IPv6 NAT support

Signed-off-by: Patrick McHardy <kaber@trash.net>
diff --git a/net/core/secure_seq.c b/net/core/secure_seq.c
index 99b2596..e61a8bb 100644
--- a/net/core/secure_seq.c
+++ b/net/core/secure_seq.c
@@ -76,6 +76,7 @@
 
 	return hash[0];
 }
+EXPORT_SYMBOL(secure_ipv6_port_ephemeral);
 #endif
 
 #ifdef CONFIG_INET