netfilter: nf_ct_pptp: fix DNATed PPTP connection address translation

When both the server and the client are NATed, the set-link-info control
packet containing the peer's call-id field is not properly translated.

I have verified that it was working in 2.6.16.13 kernel previously but
due to rewrite, this scenario stopped working (Not knowing exact version
when it stopped working).
Signed-off-by: Sanket Shah <sanket.shah@elitecore.com>
Signed-off-by: Patrick McHardy <kaber@trash.net>

net/netfilter/nf_conntrack_pptp.c

@@ -364,6 +364,7 @@ pptp_inbound_pkt(struct sk_buff *skb,
 		break;
 
 	case PPTP_WAN_ERROR_NOTIFY:
+	case PPTP_SET_LINK_INFO:
 	case PPTP_ECHO_REQUEST:
 	case PPTP_ECHO_REPLY:
 		/* I don't have to explain these ;) */