netfilter: nfnetlink_log: fix mac address for 6in4 tunnels

netfilter: nfnetlink_log: fix mac address for 6in4 tunnels

commit 0c36b48b36dc84d4215dc9d1cde1bda829214ba6 upstream.

For tunnelled ipv6in4 packets, the LOG target (xt_LOG.c) adjusts
the start of the mac field to start at the ethernet header instead
of the ipv4 header for the tunnel. This patch conforms what is
passed by the NFLOG target through nfnetlink to what the LOG target
does. Code borrowed from xt_LOG.c.

Signed-off-by: Bob Hockney <bhockney@ix.netcom.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>