netfilter: ipvs: don't check for presence of nat extension

Check for the NAT status bits, they are set once conntrack needs NAT in source or
reply direction, this is slightly faster than nfct_nat() as that has to check the
extension area.

Signed-off-by: Florian Westphal <fw@strlen.de>

net/netfilter/ipvs/ip_vs_ftp.c

@@ -260,7 +260,7 @@ static int ip_vs_ftp_out(struct ip_vs_app *app, struct ip_vs_conn *cp,
 		buf_len = strlen(buf);
 
 		ct = nf_ct_get(skb, &ctinfo);
-		if (ct && !nf_ct_is_untracked(ct) && nfct_nat(ct)) {
+		if (ct && !nf_ct_is_untracked(ct) && (ct->status & IPS_NAT_MASK)) {
 			/* If mangling fails this function will return 0
 			 * which will cause the packet to be dropped.
 			 * Mangling can only fail under memory pressure,