batman-adv: add blank line between declarations and the rest of the code

Reported by checkpatch with the following message:
"WARNING: Missing a blank line after declarations"

Signed-off-by: Antonio Quartulli <antonio@meshcoding.com>
Signed-off-by: Marek Lindner <mareklindner@neomailbox.ch>

diff --cc net/batman-adv/debugfs.c
Simple merge

diff --cc net/batman-adv/distributed-arp-table.c
Simple merge

diff --cc net/batman-adv/network-coding.c
Simple merge

diff --cc net/batman-adv/sysfs.c
Simple merge