bridge: message age needs to increase, not decrease.

commit bridge: send proper message_age in config BPDU
added this gem:
  bpdu.message_age = (jiffies - root->designated_age)
  p->designated_age = jiffies + bpdu->message_age;
Notice how bpdu->message_age is negated when reassigned to
bpdu.message_age. This causes message age to decrease breaking the
STP protocol.
Signed-off-by: NJoakim Tjernlund <Joakim.Tjernlund@transmode.se>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/bridge/br_stp.c

@@ -186,7 +186,7 @@ static void br_record_config_information(struct net_bridge_port *p,
 	p->designated_cost = bpdu->root_path_cost;
 	p->designated_bridge = bpdu->bridge_id;
 	p->designated_port = bpdu->port_id;
-	p->designated_age = jiffies + bpdu->message_age;
+	p->designated_age = jiffies - bpdu->message_age;
 
 	mod_timer(&p->message_age_timer, jiffies
 		  + (p->br->max_age - bpdu->message_age));