batman-adv: Return reason for failure in batadv_check_unicast_packet()
batadv_check_unicast_packet() is changed to return a value based on the
reason to drop the packet, which will be useful information for
future users of batadv_check_unicast_packet().
Signed-off-by: Martin Hundebøll <martin@hundeboll.net> Acked-by: Antonio Quartulli <ordex@autistici.org> Signed-off-by: Marek Lindner <lindner_marek@yahoo.de> Signed-off-by: Antonio Quartulli <ordex@autistici.org>