batman-adv: fix gateway client style issues

commit 0511575c4d03 ("batman-adv: remove obsolete deleted attribute for
gateway node") incorrectly added an empy line and forgot to remove an
include.

Signed-off-by: Simon Wunderlich <sw@simonwunderlich.de>
Signed-off-by: Marek Lindner <mareklindner@neomailbox.ch>
Signed-off-by: Antonio Quartulli <antonio@meshcoding.com>