batman-adv: Fix spelling mistakes

Fix some spelling mistakes in comments:
containg  ==> containing
dont  ==> don't
datas  ==> data
brodcast  ==> broadcast

Signed-off-by: Zheng Yongjun <zhengyongjun3@huawei.com>
Signed-off-by: Sven Eckelmann <sven@narfation.org>
Signed-off-by: Simon Wunderlich <sw@simonwunderlich.de>