bridge: multicast: add a comment to br_port_state_selection about blocking state

Add a comment to explain why we're not disabling port's multicast when it
goes in blocking state. Since there's a check in the timer's function which
bypasses the timer if the port's in blocking/disabled state, the timer will
simply expire and stop without sending more queries.
Suggested-by: NHerbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: NNikolay Aleksandrov <nikolay@cumulusnetworks.com>
Acked-by: NHerbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/bridge/br_stp.c

@@ -463,6 +463,10 @@ void br_port_state_selection(struct net_bridge *br)
 
 		if (p->state != BR_STATE_BLOCKING)
 			br_multicast_enable_port(p);
+		/* Multicast is not disabled for the port when it goes in
+		 * blocking state because the timers will expire and stop by
+		 * themselves without sending more queries.
+		 */
 		if (p->state == BR_STATE_FORWARDING)
 			++liveports;
 	}