batman-adv: Add lockdep assert for container_list_lock

The batadv_tvlv_container* functions state in their kernel-doc that they
require tvlv.container_list_lock. Add an assert to automatically detect
when this might have been ignored by the caller.

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