batman-adv: Use inline kernel-doc for enum/struct

The inline kernel-doc comments make it easier to keep changes to the
struct/enum synchronized with the documentation of the it. And it makes it
easier for larger structures like struct batadv_priv to read the
documentation inside the code.

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