batman-adv: Move definition of atomic_dec_not_zero() into main.h

atomic_dec_not_zero() is very useful and it is currently defined
multiple times. So it is possible to move it in main.h

Signed-off-by: Antonio Quartulli <ordex@autistici.org>
Signed-off-by: Sven Eckelmann <sven@narfation.org>
diff --git a/net/batman-adv/main.h b/net/batman-adv/main.h
index dc24869..ace7285 100644
--- a/net/batman-adv/main.h
+++ b/net/batman-adv/main.h
@@ -175,4 +175,6 @@
 	return (memcmp(data1, data2, ETH_ALEN) == 0 ? 1 : 0);
 }
 
+#define atomic_dec_not_zero(v)	atomic_add_unless((v), -1, 0)
+
 #endif /* _NET_BATMAN_ADV_MAIN_H_ */