batman-adv: fix local TT check for outgoing arp requests in DAT

Change introduced by 88e48d7b
("batman-adv: make DAT drop ARP requests targeting local clients")
implements a check that prevents DAT from using the caching
mechanism when the client that is supposed to provide a reply
to an arp request is local.

However change brought by be1db4f6
("batman-adv: make the Distributed ARP Table vlan aware")
has not converted the above check into its vlan aware version
thus making it useless when the local client is behind a vlan.

Fix the behaviour by properly specifying the vlan when
checking for a client being local or not.

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