batman-adv: fix DAT candidate selection (must use vid)

Now that DAT is VLAN aware, it must use the VID when
computing the DHT address of the candidate nodes where
an entry is going to be stored/retrieved.

Fixes: be1db4f6 ("batman-adv: make the Distributed ARP Table vlan aware")
Signed-off-by: Antonio Quartulli <a@unstable.cc>
[sven@narfation.org: fix conflicts with current version]
Signed-off-by: Sven Eckelmann <sven@narfation.org>
Signed-off-by: Marek Lindner <mareklindner@neomailbox.ch>