batman-adv: Fix conditional statements indentation

commit 29b9256e6631 ("batman-adv: consider outgoing interface in OGM
sending") incorrectly indented the interface check code.

Signed-off-by: Sven Eckelmann <sven@narfation.org>
Signed-off-by: Marek Lindner <mareklindner@neomailbox.ch>
Signed-off-by: Antonio Quartulli <antonio@meshcoding.com>