batman-adv: set the TAG flag for the vid passed to BLA

When receiving or sending a packet a packet on a VLAN, the
vid has to be marked with the TAG flag in order to make any
component in batman-adv understand that the packet is coming
from a really tagged network.

This fix the Bridge Loop Avoidance behaviour which was not
able to send announces over VLAN interfaces.

Introduced by 0b1da1765fdb00ca5d53bc95c9abc70dfc9aae5b
("batman-adv: change VID semantic in the BLA code")

Signed-off-by: Antonio Quartulli <antonio@open-mesh.org>
Acked-by: Simon Wunderlich <siwu@hrz.tu-chemnitz.de>
Signed-off-by: Marek Lindner <mareklindner@neomailbox.ch>