batman-adv: Prefix bridge_loop_avoidance local static functions with …

…batadv_

All non-static symbols of batman-adv were prefixed with batadv_ to avoid
collisions with other symbols of the kernel. Other symbols of batman-adv
should use the same prefix to keep the naming scheme consistent.

Signed-off-by: Sven Eckelmann <sven@narfation.org>