batman-adv: Avoid bool in structures

Using the bool type for structure member is considered inappropriate [1]
for the kernel. Its size is not well defined (but usually 1 byte but maybe
also 4 byte).

[1] https://lkml.org/lkml/2017/11/21/384



Signed-off-by: Sven Eckelmann <sven@narfation.org>
Signed-off-by: Simon Wunderlich <sw@simonwunderlich.de>