netfilter: nf_ct_h323: fix bug in rtcp natting

The nat_rtp_rtcp hook takes two separate parameters port and rtp_port.

port is expected to be the real h245 address (found inside the packet).
rtp_port is the even number closest to port (RTP ports are even and
RTCP ports are odd).

However currently, both port and rtp_port are having same value (both are
rounded to nearest even numbers).

This works well in case of openlogicalchannel with media (RTP/even) port.

But in case of openlogicalchannel for media control (RTCP/odd) port,
h245 address in the packet is wrongly modified to have an even port.

I am attaching a pcap demonstrating the problem, for any further analysis.

This behavior was introduced around v2.6.19 while rewriting the helper.
Signed-off-by: Jagdish Motwani <jagdish.motwani@elitecore.com>
Signed-off-by: Sanket Shah <sanket.shah@elitecore.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/nf_conntrack_h323_main.c

@@ -270,9 +270,8 @@ static int expect_rtp_rtcp(struct sk_buff *skb, struct nf_conn *ct,
 		return 0;
 
 	/* RTP port is even */
-	port &= htons(~1);
-	rtp_port = port;
-	rtcp_port = htons(ntohs(port) + 1);
+	rtp_port = port & ~htons(1);
+	rtcp_port = port | htons(1);
 
 	/* Create expect for RTP */
 	if ((rtp_exp = nf_ct_expect_alloc(ct)) == NULL)