bridge: mcast: do nothing if port's multicast_router is set to the same val

This is needed for the upcoming temporary port router. There's no point
to go through the logic if the value is the same.
Signed-off-by: NNikolay Aleksandrov <nikolay@cumulusnetworks.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/bridge/br_multicast.c

@@ -1853,7 +1853,10 @@ int br_multicast_set_port_router(struct net_bridge_port *p, unsigned long val)
 	int err = -EINVAL;
 
 	spin_lock(&br->multicast_lock);
-
+	if (p->multicast_router == val) {
+		err = 0;
+		goto unlock;
+	}
 	switch (val) {
 	case MDB_RTR_TYPE_DISABLED:
 		p->multicast_router = MDB_RTR_TYPE_DISABLED;