batman-adv: Store modification counter via hash helpers
Multiple datastructures use the hash helper functions to add and remove
entries from the simple hlist based hashes. These are often also dumped to
userspace via netlink and thus should have a generation sequence counter.
Reported-by: Matthias Schiffer <mschiffer@universe-factory.net> Signed-off-by: Sven Eckelmann <sven@narfation.org> Signed-off-by: Simon Wunderlich <sw@simonwunderlich.de>