batman-adv: Print correct function names in dbg messages

The function names in batman-adv changed slightly in the past. But some of
the debug messages were not updated correctly and therefore some messages
were incorrect. To avoid this in the future, these kind of messages should
use __func__ to automatically print the correct function name.

Signed-off-by: Sven Eckelmann <sven@narfation.org>
Signed-off-by: Simon Wunderlich <sw@simonwunderlich.de>