[BRIDGE]: Fix deadlock in br_stp_disable_bridge

Looks like somebody forgot to use the _bh spin_lock variant. We ran into a 
deadlock where br->hello_timer expired while br_stp_disable_br() walked 
br->port_list. 
Signed-off-by: NAdrian Drzewiecki <z@drze.net>
Signed-off-by: NStephen Hemminger <shemminger@osdl.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/bridge/br_stp_if.c

@@ -67,7 +67,7 @@ void br_stp_disable_bridge(struct net_bridge *br)
 {
 	struct net_bridge_port *p;
 
-	spin_lock(&br->lock);
+	spin_lock_bh(&br->lock);
 	list_for_each_entry(p, &br->port_list, list) {
 		if (p->state != BR_STATE_DISABLED)
 			br_stp_disable_port(p);
@@ -76,7 +76,7 @@ void br_stp_disable_bridge(struct net_bridge *br)
 
 	br->topology_change = 0;
 	br->topology_change_detected = 0;
-	spin_unlock(&br->lock);
+	spin_unlock_bh(&br->lock);
 
 	del_timer_sync(&br->hello_timer);
 	del_timer_sync(&br->topology_change_timer);