netfilter: log: netns NULL ptr bug when calling from conntrack

Since (69b34fb netfilter: xt_LOG: add net namespace support
for xt_LOG), we hit this:

[ 4224.708977] BUG: unable to handle kernel NULL pointer dereference at 0000000000000388
[ 4224.709074] IP: [<ffffffff8147f699>] ipt_log_packet+0x29/0x270

when callling log functions from conntrack both in and out
are NULL i.e. the net pointer is invalid.

Adding struct net *net in call to nf_logfn() will secure that
there always is a vaild net ptr.

Reported as netfilter's bugzilla bug 818:
https://bugzilla.netfilter.org/show_bug.cgi?id=818

Reported-by: Ronald <ronald645@gmail.com>
Signed-off-by: Hans Schillstrom <hans@schillstrom.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
diff --git a/net/netfilter/nf_log.c b/net/netfilter/nf_log.c
index 757951d..3b18dd1 100644
--- a/net/netfilter/nf_log.c
+++ b/net/netfilter/nf_log.c
@@ -148,7 +148,7 @@
 		va_start(args, fmt);
 		vsnprintf(prefix, sizeof(prefix), fmt, args);
 		va_end(args);
-		logger->logfn(pf, hooknum, skb, in, out, loginfo, prefix);
+		logger->logfn(net, pf, hooknum, skb, in, out, loginfo, prefix);
 	}
 	rcu_read_unlock();
 }