batman-adv: Remove unnecessary INIT_HLIST_NODE() calls

There's no need to for an explicit hlist_node initialization if it is
added to a list right away, like it's the case with the
hlist_add_head()s here.

Signed-off-by: Linus Lüssing <linus.luessing@web.de>
Signed-off-by: Marek Lindner <lindner_marek@yahoo.de>
Signed-off-by: Antonio Quartulli <ordex@autistici.org>