batman-adv: Use bitwise instead of arithmetic operator for flags

This silences the following coccinelle warning:

"WARNING: sum of probable bitmasks, consider |"
Signed-off-by: NLinus Lüssing <linus.luessing@c0d3.blue>
Signed-off-by: NMarek Lindner <mareklindner@neomailbox.ch>
Signed-off-by: NSven Eckelmann <sven@narfation.org>
Signed-off-by: NSimon Wunderlich <sw@simonwunderlich.de>

net/batman-adv/multicast.c

@@ -528,7 +528,7 @@ static bool batadv_mcast_mla_tvlv_update(struct batadv_priv *bat_priv)
 	}
 
 	return !(mcast_data.flags &
-		 (BATADV_MCAST_WANT_ALL_IPV4 + BATADV_MCAST_WANT_ALL_IPV6));
+		 (BATADV_MCAST_WANT_ALL_IPV4 | BATADV_MCAST_WANT_ALL_IPV6));
 }
 
 /**