batman-adv: remove obsolete variable primary_iface from orig_node
This variable became obsolete when changing to the new bonding mechanism
based on the multi interface optimization. Since its not used anywhere,
remove it.
Reported-by: Linus Lüssing <linus.luessing@web.de> Signed-off-by: Simon Wunderlich <sw@simonwunderlich.de> Signed-off-by: Marek Lindner <mareklindner@neomailbox.ch> Signed-off-by: Antonio Quartulli <antonio@meshcoding.com>