bridge: define some min/max/default ageing time constants

Signed-off-by: Scott Feldman <sfeldma@gmail.com>
Acked-by: Jiri Pirko <jiri@resnulli.us>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/bridge/br_device.c b/net/bridge/br_device.c
index 6ed2feb..2f81624 100644
--- a/net/bridge/br_device.c
+++ b/net/bridge/br_device.c
@@ -391,7 +391,7 @@
 	br->bridge_max_age = br->max_age = 20 * HZ;
 	br->bridge_hello_time = br->hello_time = 2 * HZ;
 	br->bridge_forward_delay = br->forward_delay = 15 * HZ;
-	br->ageing_time = 300 * HZ;
+	br->ageing_time = BR_DEFAULT_AGEING_TIME;
 
 	br_netfilter_rtable_init(br);
 	br_stp_timer_init(br);