resubmit bridge: fix message_age_timer calculation

This changes the message_age_timer calculation to use the BPDU's max age as
opposed to the local bridge's max age.  This is in accordance with section
8.6.2.3.2 Step 2 of the 802.1D-1998 sprecification.

With the current implementation, when running with very large bridge
diameters, convergance will not always occur even if a root bridge is
configured to have a longer max age.

Tested successfully on bridge diameters of ~200.
Signed-off-by: NChris Healy <cphealy@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/bridge/br_stp.c

@@ -209,7 +209,7 @@ static void br_record_config_information(struct net_bridge_port *p,
 	p->designated_age = jiffies - bpdu->message_age;
 
 	mod_timer(&p->message_age_timer, jiffies
-		  + (p->br->max_age - bpdu->message_age));
+		  + (bpdu->max_age - bpdu->message_age));
 }
 
 /* called under bridge lock */