ipvs: remove IPS_NAT_MASK check to fix passive FTP

The IPS_NAT_MASK check in 4.12 replaced previous check for nfct_nat()
which was needed to fix a crash in 2.6.36-rc, see
commit 7bcbf81a ("ipvs: avoid oops for passive FTP").
But as IPVS does not set the IPS_SRC_NAT and IPS_DST_NAT bits,
checking for IPS_NAT_MASK prevents PASV response to be properly
mangled and blocks the transfer. Remove the check as it is not
needed after 3.12 commit 41d73ec0 ("netfilter: nf_conntrack:
make sequence number adjustments usuable without NAT") which
changes nfct_nat() with nfct_seqadj() and especially after 3.13
commit b25adce1 ("ipvs: correct usage/allocation of seqadj
ext in ipvs").

Thanks to Li Shuang and Florian Westphal for reporting the problem!
Reported-by: Li Shuang <shuali@redhat.com>
Fixes: be7be6e1 ("netfilter: ipvs: fix incorrect conflict resolution")
Signed-off-by: Julian Anastasov <ja@ssi.bg>
Acked-by: Simon Horman <horms@verge.net.au>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

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 && (ct->status & IPS_NAT_MASK)) {
+		if (ct) {
 			bool mangled;
 
 			/* If mangling fails this function will return 0