batman-adv: remove unsed argument from batadv_dbg_arp() function

The argument "type" passed to the batadv_dbg_arp() function is
never used. Remove it.

Signed-off-by: Antonio Quartulli <a@unstable.cc>
Signed-off-by: Sven Eckelmann <sven@narfation.org>
Signed-off-by: Simon Wunderlich <sw@simonwunderlich.de>