batman-adv: Check return value of try_module_get

New operations should not be started when they need an increased module
reference counter and try_module_get failed.

This patch addresses Coverity #712284: Unchecked return value

Signed-off-by: Sven Eckelmann <sven@narfation.org>
Signed-off-by: Antonio Quartulli <ordex@autistici.org>

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

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

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

diff --cc net/batman-adv/main.h
Simple merge