batman-adv: Include main.h in bat_v_ogm.h

main.h includes statements which (re)define preprocessor variables which
influence the compiled code. This makes it necessary to include it in all
files. For example, it redefines pr_fmt used to the module as prefix for
each pr_* message.

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