bridge: return boolean instead of integer in br_multicast_is_router

Return statements in functions returning bool should use
true/false instead of 1/0.

This issue was detected with the help of Coccinelle.

Fixes: 85b35269 ("bridge: Fix build error when IGMP_SNOOPING is not enabled")
Signed-off-by: NGustavo A. R. Silva <garsilva@embeddedor.com>
Reviewed-by: NStephen Hemminger <stephen@networkplumber.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/bridge/br_private.h

@@ -760,7 +760,7 @@ static inline void br_multicast_flood(struct net_bridge_mdb_entry *mdst,
 
 static inline bool br_multicast_is_router(struct net_bridge *br)
 {
-	return 0;
+	return false;
 }
 
 static inline bool br_multicast_querier_exists(struct net_bridge *br,