batman-adv: Fix indentation of batadv_seq_before

Also multiline macros should have their statements start on a tabstop. This
was detected by checkpatch.pl after commit a134f8de

 ("checkpatch:
improve the TABSTOP test to include declarations").

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