batman-adv: always run purge_orig_neighbors

The current code will not execute batadv_purge_orig_neighbors() when an
orig_ifinfo has already been purged. However we need to run it in any
case. Fix that.

This is a regression introduced by
7351a482
("batman-adv: split out router from orig_node")

Signed-off-by: Simon Wunderlich <simon@open-mesh.com>
Signed-off-by: Marek Lindner <mareklindner@neomailbox.ch>
Signed-off-by: Antonio Quartulli <antonio@meshcoding.com>