batman-adv: Provide bla group in the mesh_info netlink msg

The bridge loop avoidange is the main information for the debugging of of
bridge loop detection problems. It is therefore necessary when comparing
the bla claim tables.

Signed-off-by: Sven Eckelmann <sven@narfation.org>
Signed-off-by: Simon Wunderlich <sw@simonwunderlich.de>
Signed-off-by: Marek Lindner <mareklindner@neomailbox.ch>