Staging: batman-adv: fix batman icmp originating from secondary interface

If a batman icmp packet had to be routed over a secondary interface
at the first hop, the mac address of that secondary interface would
be written in the 'orig' field of the icmp packet. A node which is
more than one hop away is not aware of the mac address because
secondary interfaces are not flooded through the whole mesh and
therefore can't send a reply.
This patch always sends the mac address of the primary interface
in the 'orig' field of the icmp packet.

Signed-off-by: Marek Lindner <lindner_marek@yahoo.de>
Signed-off-by: Sven Eckelmann <sven.eckelmann@gmx.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>